Renju

Five In Line
Free multiplayer version of Gomoku. Includes rules.
http://www.fiveinline.com/

FIVE-STONE Game
A java interface that allows 2 users to play with each other.
http://www.cs.fiu.edu/~longy/five.html

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.
http://www.pente.net

Renju Offline
Intermediary for offline games. Supports Classic and Sakata rules.
http://renju.net.ru/

Stallan's Connect 5
Very fast playing Connect 5 game, written in Java. The source code is available upon request.
http://biphome.spray.se/dread/connect5.html