Best Free and Open Source Software, and Many More

posted by Rianne Schestowitz on Sep 20, 2026

• Best Free and Open Source Alternatives to Microsoft Authenticator

  Microsoft’s stance for decades was that community creation and sharing of communal code (later to be known as free and open source software) represented a direct attack on their business. Their battle with Linux stretches back many years. Back in 2001, former Microsoft CEO Steve Ballmer famously tarnished Linux “a cancer that attaches itself in an intellectual property sense to everything it touches”. Microsoft also initiated its “Get the Facts” marketing campaign from mid-2003, which specifically criticized Linux server usage, total cost of ownership, security, indemnification and reliability. The campaign was widely criticized for spreading misinformation.

  However, in recent years, there has been a partial shift by Microsoft to embrace the open source software paradigm.

  This series looks at the best free and open source alternatives to products and services offered by Microsoft.

• Cuckoo3 - automated malware analysis sandbox

  Cuckoo3 is an automated malware analysis system for examining suspicious files and links inside controlled virtualised environments.

  The software runs on a Linux host and executes submitted material in isolated Windows sandboxes, recording what happens during the analysis and assembling observations into reports for investigation. It is aimed at malware researchers, incident responders and security teams that need to study behaviour rather than rely only on signatures or static inspection. Its modular design separates analysis, processing, storage and the web-facing workflow.

  This is free and open source software.

• Slob Dictionary - flexible GTK dictionary application

  Slob Dictionary is a desktop dictionary application built with GTK 4 and Libadwaita.

  It is designed for exploring local dictionary collections through a single polished interface, even when the source material comes in very different formats. Rather than tying users to one dictionary ecosystem, it can work with SLOB files directly and convert many other formats when necessary. Definitions can contain rich HTML or Markdown content, making it suitable for everything from straightforward word lists to complex reference works.

  This is free and open source software.

• REDasm – cross-platform disassembler and binary analysis tool

  REDasm is a cross-platform disassembler and binary analysis tool for examining compiled programs. It combines a native Qt interface with a separate analysis engine, giving reverse engineers an interactive environment without tying the underlying analysis facilities to the graphical frontend.

  The architecture is extensible, with processor support and executable loaders implemented as plugins. REDasm also gives unusual attention to retro and legacy executable formats alongside contemporary binaries, making it relevant for software preservation as well as conventional reverse engineering.

  This is free and open source software.

• Dogtag PKI - enterprise certificate authority suite

  Dogtag is suited to centralised environments where certificates and cryptographic keys must be administered according to organisational policies. It can form the basis of relatively sophisticated deployments involving multiple authorities, replicated services and protected key storage.

  Dogtag’s breadth makes it more appropriate for substantial PKI installations than for users simply looking to create a small local certificate authority.

  This is free and open source software.

• IQmol3 - molecular editor and visualization package

  Its visualization capabilities include molecular surfaces such as electron densities and molecular orbitals. IQmol3 can also animate vibrational frequencies and reaction pathways, making it useful for examining how structures and calculated properties change during a calculation. The application can display several kinds of molecular data and is intended to provide an interactive graphical environment rather than a command-only workflow.

  Q-Chem jobs can be run locally or submitted to remote systems over SSH. The networking code includes host-key handling and support for tracking submitted jobs, which makes IQmol3 useful when calculations are carried out on a separate workstation or compute server rather than the local desktop.

  This is free and open source software.

• cavif - convert PNG and JPEG images to AVIF

  It uses the rav1e AV1 encoder through the ravif crate and is implemented entirely in Rust. The program is aimed at users who want a compact, scriptable way to produce modern AVIF assets without relying on a heavyweight graphics application. It can process individual files or groups of images and writes AVIF output alongside the source by default. AVIF is well suited to web publishing and modern image-delivery pipelines, while cavif keeps the conversion workflow deliberately straightforward. Its defaults are intended to provide sensible colour and bit-depth choices without requiring codec-specific tuning.

  This is free and open source software.

• CDK – cheminformatics and bioinformatics toolkit

  CDK also provides extensive facilities for chemical structure searching and comparison. These include exact structure searching, SMARTS and substructure matching, together with molecular fingerprint implementations such as ECFP, MACCS and Daylight-style fingerprints. Developers can calculate QSAR and other molecular descriptors, generate two-dimensional coordinates and render chemical structures.

  Reaction processing is supported alongside facilities for stereochemistry, atom and bond properties, structure normalisation and chemical transformations. The toolkit is modular, so applications can depend only on the components they need, while Maven users can also use the complete CDK bundle.

  This is free and open source software.

• XCA - graphical certificate and key management

  XCA can also help maintain consistency when issuing groups of certificates. Reusable templates let administrators establish common certificate properties and apply them when generating new certificates or requests.

  Its import and export facilities make the application useful beyond running a CA. Existing certificates and keys can be brought into the database for inspection and organisation, while objects can be exported in formats suitable for other applications and services.

  XCA is built with Qt and OpenSSL and provides native support for Linux. It offers a relatively approachable interface while retaining access to detailed certificate and key-management operations.

  This is free and open source software.

• ScanCode Toolkit - scan code for licenses and software components

  ScanCode Toolkit is a collection of code-analysis tools for identifying the origin and composition of a software codebase.

  It examines source and binary files for licensing, copyright, package, dependency and vulnerability information. This makes it useful for open source compliance, software composition analysis, due diligence and constructing detailed software inventories. ScanCode is designed for deep scanning rather than simply reading a package manifest, and its licensing engine compares detected material against a substantial collection of known license texts and rules. The toolkit can be operated from the command line or embedded as a Python library.

  This is free and open source software.

• Focalors - offline chess engine and learning application

  The application uses two different evaluation systems. An NNUE network provides the evaluation used during chess engine search, while a separate hand-crafted evaluation runs alongside it when Focalors needs to explain what is happening in a position. This lets the program describe identifiable chess concepts rather than relying solely on a numerical engine score.

  For example, the explanatory evaluation can identify issues such as hanging pieces, weakening king safety and deterioration of pawn structure. This is intended to make computer-assisted analysis more useful to players who want to understand why a move caused problems rather than simply discover which move the engine preferred.

  Focalors can also generate training puzzles from mistakes made in the user’s own games. Positions that caused difficulties during normal play can therefore be turned into material for later practice. Games, progress and statistics are stored locally in a small SQLite database.

  This is free and open source software.

• tuidict – fast FreeDict dictionary TUI

  tuidict is a keyboard-driven dictionary application with a text user interface.

  It uses dictionaries from FreeDict, giving users access to multiple language pairs without building a dictionary collection manually. Dictionaries are downloaded from inside the application and then stored locally for repeated use. The interface is split into translation, dictionary management and download views, keeping searching and collection maintenance separate. Its emphasis is on immediate lookup: typing updates results live, while a prefix-oriented data structure keeps searches responsive even with sizeable dictionaries.

  This is free and open source software.

• Easy-RSA - command-line PKI management utility

  Its command-line approach makes it well suited to systems without a graphical environment and to administrators who want certificate-management procedures that can be documented or incorporated into scripts.

  Easy-RSA deliberately concentrates on the core tasks involved in operating a certificate authority. It does not try to provide the web interfaces, workflow engines or distributed services found in enterprise PKI suites. This keeps the software relatively lightweight and gives administrators direct access to the files and structures underpinning their certificate authority.

  The utility is particularly useful where OpenSSL provides the required cryptographic functionality but its lower-level commands would make routine CA administration unnecessarily cumbersome.

  This is free and open source software.

• dictd – dictionary database server for the DICT protocol

  dictd is a dictionary database server implementing the Dictionary Server Protocol (DICT).

  The protocol uses TCP transactions to give clients a uniform way to request definitions and search word indexes across multiple natural-language dictionary databases. This makes dictd useful when several dictionaries need to be exposed through one consistent network interface rather than accessed independently. Databases are distributed separately from the server, so administrators can choose which collections to provide and configure how clients reach them.

  This is free and open source software.

• sigtool – file signing and encryption utility

  It combines Ed25519 signatures with multi-recipient public-key encryption, providing a workflow reminiscent of tools such as signify and age while also exposing its functionality as a Go package. The command-line program can generate keys, sign files, verify signatures, encrypt data for one or more recipients, and decrypt it again.

  A particularly useful feature is its support for existing OpenSSH Ed25519 keys, allowing users to work with established SSH identities instead of maintaining a completely separate key set. Encryption can optionally authenticate the sender as well as protect the file contents.

  This is free and open source software.