Forge has more than 3,000 cards and allows to you play the trading card game Magic: The Gathering against the computer with rules enforcement. Other formats include drafting, sealed deck, and the "quest mode" where you start with a basic deck and you win more cards. The AI and user interface are basic but usable.
TrueSculpt lets you sculpt a 3D virtual clay ball by pushing and pulling it with your fingers. Many different tools are available for easy modeling: draw, grab, smooth, flatten, paint, symmetry, etc. TrueSculpt features undo/redo and the standard ".obj" save format. You can zoom and pan with two fingers.
PalindromicPrimeFinder is a little "toy" program that can find relatively big (e.g. 1000-2000 digits) palindromic probable prime (PRP) numbers. It generates random palindromic numbers and tests them for primality using a probabilistic algorithm. It is multi-threaded and stops after a certain timeout (if no palindromic primes are found).