Five In Line: Free multiplayer version of Gomoku. Includes rules.
FIVE-STONE Game: A java interface that allows 2 users to play with each other.
Pente Net: Play Pente against a friend anywhere in the world! Pente Net supplies the board, the stones, the rules, the game system for you. No downloads required. Compatible with all browsers, WebTV.
Renju Offline: Intermediary for offline games. Supports Classic and Sakata rules.
Stallan's Connect 5: Very fast playing Connect 5 game, written in Java. The source code is available upon request.