Browser Based

Bots
A text based fighting simulator taking on the roll of a Robot.
http://www.bots2.net/

KillStreet.com
Free Text based fighting simulator under the roll of a modern thug.
http://killstreet.com

Kung Fu Madness
Kung Fu fighting game. Challenge other players in battle and team up with others by joining a dojo.
http://www.kungfumadness.com/

Prison Struggle
Free text based game where users take on the roll of a prison inmate.
http://www.prisonstruggle.com

RetroUrban
Flash based fighting game.
http://www.retrourban.com

TheNinja-RPG.com
Browser based fighting simulator taking on the roll of a Ninja.
http://theninja-rpg.com/

The Wrestling Game
Roleplaying-based on fighting and career management, titles, tournaments, rosters, and federations. [Registration required.]
http://www.thewrestlinggame.com/

Xenyoo
Player creates a character which you train and make stronger to fight against other players.
http://www.xenyoo1.com/