Calc is arbitrary precision arithmetic system that uses a C-like language. It's useful as a calculator, an algorithm prototype, and as a mathematical research tool. More importantly, calc provides a machine-independent means of computation. Calc comes with a rich set of builtin mathematical and programmatic functions.
Freeciv is a multiuser reimplementation for Unix/X of the famous Microprose game of Civilization. By default, the game is an improved Civ II, but this can be customized; modpacks for near-100% compatibility with Civ I and Civ II are included. Multiuser gameplay is real-time: in each turn, all human players move concurrently. The game is designed to remain fairly playable even on poor network connections. Freeciv can also be played on standalone machines, and its AI players are a good challenge for beginners. The source code comes with the server, two X clients, and non-X clients for MS Windows and Amiga. Freeciv is released under the GNU General Public License. It is maintained by an international team of coders and enthusiasts, and is easily one of the most fun and addictive network games out there.
JExpress is a Java installer builder and auto-updater. It gives you your choice of a standalone installer, including both native and cross platform installers and updaters for Windows, Mac OS X, Linux, and Solaris, or a Java Web Start one-click install. You create your installer quickly with your choice of a simple wizard or a powerful advanced interface, both included. You can bundle the exact JVM you want with your installer. The auto-updater gives you a continuous revenue stream after the sale. Your software is always up-to-date, so your customers have fewer problems. You also get all the features you expect in a top end installer. Your Java application becomes a native program just like any other. On Windows it's an EXE, on Mac OS X an app bundle, etc. If you need something really special, you can customize your installer by adding simple Java classes. You can even get a source license at a reasonable price.
Nets is a flexible and extensible network inventory and asset management system that works on all Unix and Windows platforms, and works with most SQL databases. Its complete GUI allows you to maintain details of your entire network, from network links down to interfaces and routers. It assists in provisioning, costing, reporting, and maintaining network details. It includes a network browser, an extension API, and plugins for IP address map visualisation, reports, schematics.
PLIB is a set of libraries to write games and other realtime interactive applications that are 100% portable across a wide range of hardware and operating systems. It's used by Majik3D, FlightGear, and others, and includes libraries for GUI widgets, sound replay, geometry, scene graph, joystick, and fonts/text.
wxDesigner is a dialog editor and RAD tool for the wxWindows C++ library and its popular Python and Perl bindings. It includes a visual dialog editor, a bitmap editor, a syntax-highlighting source editor, and built-in mechanisms for automatic generation of file skeletons, GUI classes, event handlers, and getter functions. It provides an identical user interface and identical functionality for C++, Perl, and Python, and it can generate output in C++, Python, Perl, and XML.
Atari800 is an Atari 8-bit computer (400, 800, and XL and XE series) and Atari 5200 game system emulator for DOS, Windows, Amiga, Atari ST, Mac, and Linux/UNIX. It includes support for Atari cartridge ROMs, popular Atari disk images files, running Atari binaries directly from the host system, and accessing the host filesystem from within the emulated Atari.
TuxKart is a 3D GoKart racing game with several famous OpenSource mascots participating. The game uses PLIB and OpenGL, and is portable to a wide range of OS's. There are several racecourses provided, with full information on how to add your own. Except for a few minor details, this game is essentially complete, and very playable.
PHP Mobile Mail is aimed at mobile professionals who want to use their favorite MUAs (noteably pine or mutt) on their laptop, either in UNIX or Windows (under GNU Gygwin). This lets you work offline. It includes a mail_spooler program, which accepts the output of you MUA and spools (on, or offline). When connected, another process parses through the spool and sends your messages. It is also designed to "fake" using your REAL email address with free services like gmx.net, or mail.yahoo.com, when using their POP and SMTP servers, assuming you have a domain and account that you can control to this degree.