Apps to Extensible by Plugins/Extensions

PlantUML is an open-source tool that allows users to generate a wide variety of UML and other diagram types from a simple human-readable text description. It supports sequences, use case, class, activity, component, state, object, deployment, timing diagrams, and more, making it accessible and efficient for technical documentation and visualization.

Org-mode is a powerful and flexible mode for GNU Emacs, designed for note-taking, project planning, to-do list management, and authoring documents. It utilizes simple plain text files with intuitive markup.

Nomacs is a fast and lightweight free, open-source image viewer offering a wide array of features for diverse image formats, including RAW and PSD. It provides essential editing tools, batch processing capabilities, and extensibility via plugins, making it more than just a simple viewer.

Rocket.Chat is a comprehensive free and open-source team communication platform, offering real-time chat, audio/video conferencing, screen sharing, and file sharing. Designed for flexibility, it can be self-hosted on-premises for maximum control and customization, making it ideal for organizations prioritizing data privacy and security.

Programmer's Notepad is a fast and lightweight text editor designed specifically for programmers and developers. It offers extensive syntax highlighting for numerous programming languages, a powerful search and replace engine with regular expression support, and a highly customizable environment. Ideal for those seeking a free, open-source, and portable code editing solution.

Firefox Developer Edition is a specialized version of the Firefox browser tailored for web developers. It offers the latest features and tools earlier than the standard release, providing a stable yet cutting-edge environment for building and testing websites.

KDevelop is a powerful, free, and open-source Integrated Development Environment (IDE) designed for Unix-like systems, Windows, and macOS. It offers a robust set of features for a wide range of programming languages, including C++, Python, PHP, and more, making it a versatile tool for software developers.

GNU IceCat is a free software version of the Firefox web browser, distributed by the GNU Project. It focuses on user freedom and privacy by removing proprietary components and incorporating privacy-enhancing features.

Wox is a highly customizable and extensible open-source application launcher for Windows. It allows users to quickly launch applications, search files, perform web searches, and execute commands using a simple keyword-based interface.

Claws Mail is a powerful yet lightweight, open-source email and news client built on GTK+. It's known for its speed, stability, rich feature set, and high degree of customization, making it an excellent choice for users demanding control and efficiency.

Mantis Bug Tracker is a free and open-source, web-based issue tracking system designed primarily for software defect tracking. It offers a straightforward interface and a range of features suitable for managing projects and tracking the lifecycle of bugs and issues.

rTorrent is a powerful and resource-efficient command-line BitTorrent client for Unix-like systems. Built on the advanced libTorrent library, it offers high performance and extensive configurability, making it ideal for users seeking control and automation.

Kanboard is a free and open-source Kanban project management software that streamlines task and project workflows. It offers a minimalist and visual approach to managing tasks, making it ideal for teams seeking simplicity and efficiency in their collaboration efforts.

Kopete is a versatile, free and open-source instant messaging client designed initially for the KDE Plasma desktop. It distinguishes itself by supporting a multitude of protocols, allowing users to connect to various chat networks from a single application.

Irssi is a highly customizable command-line IRC client popular among power users and system administrators for its extensibility and efficiency.

AngularJS is a powerful open-source JavaScript framework developed by Google that enables developers to build dynamic single-page applications (SPAs). It simplifies front-end development by extending HTML with its directives and facilitating two-way data binding, promoting a Model-View-Controller (MVC) or Model-View-ViewModel (MVVM) architectural pattern.

phpBB is a free and open-source bulletin board software written in the PHP programming language. It provides a robust platform for creating and managing online communities through discussion forums, enabling users to engage in conversations, share information, and build connections.

Discourse is a modern, open-source discussion platform designed for building thriving online communities. It combines elements of traditional forums, mailing lists, and chat to foster civil and engaging conversations.

AkelPad is a highly customizable, portable text editor designed for Windows. It boasts a lightweight footprint, extensive plugin support for enhanced functionality, and the ability to handle large files efficiently. Ideal for users seeking a fast and configurable alternative to standard text editors.

Wekan is a free and open-source Kanban board application designed for collaborative task management. Based on the principles of Kanban, it offers a visual way to organize work, track progress, and improve workflow efficiency for individuals and teams.

FileBot is a powerful and comprehensive tool designed for efficient file organization and renaming, specializing in media files like movies, TV shows, and anime. It automates the process of fetching accurate metadata, downloading subtitles, and managing your media library with ease.

Psi is a robust, open-source instant messaging client built on the XMPP protocol. It's known for its focus on speed, efficiency, and adherence to XMPP standards, offering a clean interface and strong privacy features for secure and reliable communication.

MythTV is a free and open-source digital video recorder (DVR) software designed to transform a Linux-based computer into a complete home media center. It allows users to watch, record, and play live television, manage their video library, listen to music, and more.

Smuxi is a feature-rich, cross-platform IRC client designed with productivity and usability in mind. Inspired by the command-line power of Irssi, it provides a graphical interface for seamless communication across multiple networks including IRC, XMPP, and Twitter.

Tiki Wiki CMS Groupware is a free and open-source, all-in-one web-based application for collaboration and management. It combines a powerful wiki engine with comprehensive features for content management, project tracking, workflow, and office functions, making it a versatile solution for diverse organizational needs.

concrete5 is a powerful open-source Content Management System (CMS) known for its ease of use, featuring in-context editing and a flexible architecture. It enables users to build and manage websites and web applications with minimal technical expertise.

KTorrent is a robust and feature-rich BitTorrent client integrated with the KDE Plasma Desktop environment. It offers a lightweight and intuitive interface for downloading and sharing files over the BitTorrent network, emphasizing user control and privacy without intrusive advertisements.

QupZilla is a free and open-source web browser designed for general users, emphasizing speed, privacy, and a clean user interface. It leverages the powerful QtWebEngine to deliver a modern browsing experience while remaining lightweight and resource-efficient.

ImpressPages is an open-source PHP framework and content management system (CMS) designed for building websites quickly and efficiently. It features a user-friendly drag-and-drop interface, a modular architecture, and includes functionalities for blogging, e-commerce, and more. Its framework core provides flexibility for developers.

K-Meleon is a fast, customizable, and lightweight open-source web browser for Windows. Utilizing the Gecko engine from Firefox, it emphasizes efficiency, user control, and a highly adaptable interface, making it ideal for users prioritizing performance and personalization.