libTISCH is a framework for easy development of multi-touch applications. It contains tools for video processing, calibration, gesture recognition and, most importantly, a GUI toolkit with widgets that utilize the multi-touch gestures detected by the lower layers. It runs on Linux, Mac OS X, and Windows.
The CRT X-Y Library (libcrtxy) allows you to write vector-based video games (like Asteroids, Lunar Lander, and Battlezone from the 1970s and 80s). The end-user (and/or packager of your software) determines how lines are rendered, depending on the capabilities of their system. This choice includes anti-aliasing, alpha blending, blurring, and even the display size and depth. Fixed-point math is used, and sine and cosine trigonometric functions (using look-up tables) are provided. The library is based on libSDL and uses SDL as the video backend.
ppDrag is a drag'n'drop plugin for jQuery, which mimics the interface of jQuery UI's Draggable. It currently supports a small subset of its options, but the implementation is different, since ppDrag focuses on performance. All major existing browsers are supported. This includes IE6/7, Firefox1/2/3, Opera, Konqueror, Safari, and others.
Green Dome GNUstepWeb for Mac OS X provides a WebObjects 4.5-like environment for Mac OS X (with some support for WO5 additions). It is composed of modified versions of the standard GNUstepBaseAdditions, GDL2, and GNUstepWeb frameworks, built to run on top of Apple's Cocoa frameworks. The GNUstep frameworks have been built with Xcode as true Mac OS X frameworks. Thus, they may be used as any other framework under Mac OS X. Note that this is a standalone package that does not require or interoperate with a separate GNUstep installation/environment. It is not intended to provide a complete GNUstep environment, such as would be expected of a full GNUstep installation.
Optnik is a CLR library to help with option parsing and command execution. It is very similar to Mono.Options but has support for sub-commands, each with its own private set of options. Optnik is written in C# and runs on Mono and MS .NET (and probably on other CLR implementations too).