Mac OS X Softwares to Extensible by Plugins/Extensions

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

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.

Sleipnir is a versatile web browser designed for seamless integration between desktop and mobile devices. Offering a range of customization options, robust privacy features, and built-in tools like an RSS reader and social media integrations, Sleipnir aims to provide a tailored browsing experience.

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.

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.

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.

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.

Google Desktop was a powerful desktop search application designed to index and rapidly locate information across your computer. It integrated seamlessly with your operating system, offering indexed search for files, emails, web history, and more, along with a customizable sidebar for widgets and gadgets.

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.

Acorn is a powerful yet accessible image editing software designed for macOS. It offers a comprehensive toolset for photo manipulation, digital drawing, and graphic design, catering to both hobbyists and professionals.

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.

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.

WebStorm is a powerful JavaScript IDE from JetBrains, designed for modern web development. It offers advanced coding assistance for JavaScript, HTML, and CSS, alongside support for many related technologies like Node.js, React, Angular, and Vue.js. Its rich feature set includes smart code completion, error detection, refactoring, debugging, and integrated development tools.

Xamarin Studio is a comprehensive IDE designed for building cross-platform applications for iOS and Android using C#. It enables developers to write native user interfaces and share significant code across platforms.

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.

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.

Espresso is a powerful macOS-only web development tool designed for speed and simplicity. It combines code editing, visual previewing, and publishing features, making it an all-in-one solution for building websites.

Jenkins is a leading open-source automation server that enables developers to reliably build, test, and deploy their software. It supports various version control systems and build tools, making it a central hub for continuous integration and continuous delivery pipelines.

Emby is a powerful, open-source media server that revolutionizes how you access and enjoy your personal media collection. It organizes your movies, TV shows, music, and photos into a visually stunning and easily navigable interface, streaming them seamlessly to practically any device, anywhere.

Yandex.Browser is a secure and feature-rich web browser based on the Chromium project, offering a blend of performance, privacy tools, and unique functionalities for an enhanced browsing experience.

muCommander is a versatile, open-source file manager designed for productivity across various operating systems. It offers a dual-pane interface for efficient file operations, built-in support for network protocols like FTP and SSH, and extensive customization options, making it a powerful tool for both casual users and power users who need advanced file management capabilities.

ConceptDraw PRO is a versatile diagramming tool designed for creating professional business graphics, flowcharts, mind maps, project diagrams, and more. It provides a comprehensive set of tools and libraries for visual communication and project management.

fre:ac is a free audio converter and CD ripper supporting popular audio formats such as MP3, MP4, Ogg Vorbis, FLAC, AAC, and Bonk. It's available for Windows, macOS, Linux, and FreeBSD and is released under the GNU General Public License.