0 A.D. (pronounced "zero ey-dee") is a cross-platform real-time strategy (RTS) game of ancient warfare. It's a historically-based war/economy game that allows players to relive or rewrite the history of ancient civilizations, each depicted at their peak of economic growth and military prowess.
0release is a program to generate source and binary releases automatically. With minimal configuration, 0release will generate a source tarball release candidate, build it to create a binary archive, upload them to your Web server, check the uploads, and tag the release in GIT and update the version number. It can run unit-tests and custom actions, such as building documentation, etc. For Zero Install users, it can also upload a signed XML metadata file about the release, allowing these users to upgrade automatically. Releases are signed with your GPG key.
4K Video Downloader is a video and audio downloader for YouTube, Vimeo, Facebook, Dailymotion, Metacafe, and other video-sharing services. It features video quality up to 4k resolution, FLV, MP4, and MKV support, extraction of audio to the MP3 format, and a "Smart Mode" for fast downloads.
4store is an efficient, scalable, and stable RDF database. It was developed to underpin Semantic Web applications. It has been providing a base platform for these applications for around 3 years. It has successfully held and run queries over databases of 15GT, supporting a Web application used by hundreds of thousands of people.
4tH is a Forth compiler with a little difference. Instead of the standard Forth engine it features a conventional compiler. 4tH is a very small compiler that can create bytecode, C-embeddable bytecode, standalone executables, but also works fine as a scripting language. It supports about 95% of the ANS Forth CORE wordset and features conditional compilation, pipes, files, assertions, forward declarations, enumerations, structures, suspended execution, recursion, include files, etc. It comes with an RPN calculator, line editor, preprocessor, compiler, decompiler, C-source generator, a virtual machine, and a multitasking environment.