TouchKit: Open Source Multi-Touch
Intrigued by Microsoft Surface, but don't want to spend $10,000 - or deal with Microsoft? Then take a look at the TouchKit project, which can help you get together a table-sized screen with a multitouch interface, using open source components.
TouchKit comprises both hardware and software components. On the software side, the API is implemented as an addon to OpenFrameworks. This gives it cross-platform compatibility with OS X, Windows, and Linux, though you're going to need to be comfortable hacking around in a pre-release C++ framework to make use of it. The software is licensed LGPLv3.
On the hardware side, TouchKit consists of a computer, projector, camera, and a special screen including a rear projection surface and strings of infrared LEDs. Since you're not all that likely to have the screen laying around, the inventors will sell you the core pieces for $1580 or just the infrared strip lighting for $350.They also say they'll be releasing schematics under a Creative Commons license, making this another open hardware project. Some of the hardware schematics are already online, with more to come.
TouchKit reminds me of some of the fun hacking projects that form our heritage in the computer field, right back to the original Spacewar! If you're handy with a soldering iron and have some spare time and a bit of spare money, it could be a great project to get involved with.