What algorithms and heuristics are popular in computer chess? Computer chess has exploded in the last twenty years, with a computer world championship being established and many chess computer designers becoming quite profitable from their endeavors.  Some of the programs hide their source code, but a great many are open source, most notably Fruit, which served as the basis for a family of chess engines.  

What are some examples of heuristics or algorithms used by chess computers, and which have been most successful or are most popular?
Algorithms mainly used are based on searching the state space. The problem is that the possible positions a piece can make in the next move is very huge. But it is finite. It is basically a search problem. There is a valid position a piece can take. That is there is a known start state and a know end state. There is no probability involved like the problem of tossing a coin.
A typical algorithm is to use brute force and compute moves for a fixed number of moves. MiniMax can be used in such cases. Alpha-beta pruning is also a well know algorithm used. Mostly the search spaces are represented using a tree based data structure.
Computer program also heavily use databases containing moves, openings, end-game positions etc.