Apps to Extensible by Plugins/Extensions

qutIM is a free and open-source, multi-protocol instant messenger designed for connecting to various networks including ICQ, Jabber, Mail.Ru, IRC, and VKontakte. It offers a unified interface for managing multiple accounts and conversations.

ISPConfig is a robust, open-source hosting control panel for Linux, designed for service providers, resellers, and individuals. It simplifies the management of web servers, mail servers, DNS servers, and more, offering a comprehensive suite of tools via a user-friendly web interface.

OpenProject is a powerful, web-based open-source project management software designed for teams of all sizes. It offers comprehensive tools for managing projects, tasks, teams, and communication in one centralized platform. Ideal for organizations prioritizing collaboration, flexibility, and data control.

Portable-VirtualBox allows you to run virtual machines directly from a USB drive without requiring an installation on the host computer. It provides a convenient and portable way to access different operating systems and applications.

CKEditor is a powerful open-source WYSIWYG HTML editor designed to be embedded into web pages, providing developers with a robust solution for enabling rich text editing capabilities for their users. It transforms simple textareas into fully-featured content creation environments.

Xabber is a free and open-source XMPP (Jabber) client for Android. It provides secure and reliable instant messaging with support for various XMPP features, including encryption, group chat, and decentralized communication. Leveraging the open XMPP protocol, Xabber offers a privacy-friendly alternative to centralized messaging platforms.

ImageGlass is a lightweight, versatile image viewing application designed as a modern, fast, and user-friendly alternative to the default Windows Photo Viewer. It supports a wide range of image formats and offers essential viewing tools alongside advanced features through its extensible architecture.

VFront is a powerful and open-source web-based front-end for managing various relational databases including MySQL, PostgreSQL, SQLite, and MariaDB. It provides a user-friendly interface for performing database operations without needing command-line access.

PCMan File Manager is a highly regarded, lightweight file manager designed for speed and efficiency. It is the default file manager for the LXDE desktop environment and offers a clean interface and essential file management functionalities with low resource consumption.

Instantbird is a powerful, cross-platform instant messaging client built on Mozilla's XULRunner, leveraging the robust libpurple library from Pidgin. It supports a wide array of instant messaging protocols, offering a unified chat experience.

Orwell Dev-C++ is a free, portable, and lightweight Integrated Development Environment (IDE) specifically designed for C and C++ programming. It provides a comprehensive set of tools including a compiler, debugger, and code editor, making it an accessible option for beginners and experienced developers alike. Its portability allows developers to carry their development environment on a USB drive.

Eye of GNOME (EOG) is the default and official image viewer for the GNOME desktop environment, known for its simplicity, speed, and tight integration within the GNOME ecosystem. It provides essential image viewing capabilities with a clean interface.

Moodle is a widely adopted, open-source Learning Management System (LMS) designed to provide educators, administrators, and learners with a single, robust, and secure system to create personalized learning environments. It facilitates online learning, blended learning, and distance education with a comprehensive set of tools for course creation, delivery, and management.

Miranda NG is a highly extensible, multi-protocol instant messaging client for Windows. A successor to the popular Miranda IM, it offers a modular architecture supporting numerous chat networks, allowing users to consolidate their conversations into a single interface. It's designed for resource efficiency and deep customization.

Pandoc is a powerful command-line tool for converting documents between numerous markup formats, enabling seamless content transformation for writers, developers, and publishers. It's essential for workflows involving diverse document types, from markdown to PDF, HTML, LaTeX, and more.

LXQt is a free and open-source lightweight desktop environment for Linux and BSD systems, designed for speed, efficiency, and customization. It is built from the foundation of LXDE and Razor-qt, combining the best of both worlds to provide a modern yet resource-friendly user experience.

Qmmp is a free and open-source audio player designed for various operating systems, known for its lightweight nature and extensive customization options through plugins. It provides a familiar interface similar to classic audio players while offering modern features like streaming, media conversion, and library management.

Qt Creator is a powerful, cross-platform Integrated Development Environment (IDE) tailored for building applications with the Qt framework. It supports C++, QML, and JavaScript, offering a comprehensive suite of tools for designing UIs, writing code, debugging, and deploying software across various platforms.

Light Table is an innovative code editor designed to provide developers with instant feedback and a deeper connection to their code. It offers a clean and customizable interface, focusing on interactive development and visualizing data flow.

Mutt is a highly configurable, text-based email client for Unix-like systems. It offers powerful features for advanced users who prefer a lightweight and efficient email management experience directly from the command line.

Nightingale is a highly customizable cross-platform audio player with a focus on extensibility, featuring a beautiful interface, a wide array of supported formats, and tools like media library management, podcast playback, and integrated web browsing.

CodeLite is a free, open-source, and cross-platform Integrated Development Environment (IDE) designed specifically for C, C++, PHP, and JavaScript (Node.js) development. It provides a feature-rich environment to streamline the coding process for these languages.

Gajim is a free and open-source instant messaging client for the XMPP protocol. Built using the GTK+ toolkit, it offers a wide array of features for secure and flexible communication, including encrypted chat, group conversations, multi-protocol support via gateways, and extensive customization options.

Haroopad is a discontinued markdown-enabled document processor designed for creating web-friendly content. It offers a distraction-free writing environment with live preview and syntax highlighting, making it suitable for bloggers, writers, and developers.

Nemo is the default and highly customizable file manager for the Cinnamon desktop environment. It offers a robust set of features for managing files and folders efficiently, including multi-pane views, tabbed browsing, extensibility via plugins, and an integrated terminal for advanced users.

OpenELEC is a small, fast booting embedded operating system built specifically to turn your computer into a Kodi (XBMC) media center. It focuses on simplicity and minimal configuration for a plug-and-play home theatre experience.

Redaxscript is an exceptionally lightweight and high-performance Content Management System designed for simplicity and speed.

Gwenview is a robust and user-friendly image viewer for desktop environments, primarily known for its integration with the KDE ecosystem. It offers a clean interface and essential tools for browsing, viewing, and performing basic edits on a wide range of image formats.

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.