Texas Test'em is an easy-to-use odds calculator for Texas Hold'em Poker. Just drop a few cards into place (leaving any unknown hands empty), and the program will immediately begin calculating the chances that each hand will win or tie by the river. You can view similar results for the turn or the flop. These Monte-Carlo calculations will be accurate to the first decimal place within a few seconds, and will become increasingly accurate as time passes.
You can also switch into Push Mode to perform "Sklansky-Chubukov" calculations. Set up a situation in which you'd consider pushing all-in, and the program will calculate what your opponents would do even if they could somehow see your hand. The resulting numbers represent a very conservative baseline that can help you decide whether or not to push all-in.
Either mode handles up to nine opponents in both pre-flop and post-flop situations.