Massive Multiplayer Online

Aevum Obscurum
A wartime simulation set at the beginning of the 14th century. Contains download for a variety of platforms, documentation and discussion forum.
http://www.aevumobscurum.com/

Airsoft WarZone
Based on the Airsoft franchise. Includes client download, documentation, forums and a Java chatroom.
http://www.a-wz.com

Antarez Arena
Roman era strategy with RPG elements. Offers documentation, forums, and sign up page.
http://www.areant.net

Galactic Trader
Buy, sell, and smuggle goods and contraband while avoiding the Galactic Police. Contains screenshots.
http://www.gamingmuseum.com/gal-trader.html

Global Insanities
Browser based modern-day economic and military strategy. Includes player rankings, documentation and forums.
http://www.globalinsanities.com

Massively multiplayer online game - Wikipedia
Definition with examples and related topics.
http://en.wikipedia.org/wiki/Massively_multiplayer_online_game

Paramountcy
Medieval era empire building. Includes guides, forums, and news.
http://www.hentertainment.nl/paramountcy/

Space Federation: Galactic Conquest
Empire building game with cash prizes. Includes documentation, forums and registration page.
http://gc.gamestotal.com

Unification War
Free browser based space strategy. Offers documentation and a guide.
http://uc.gamestotal.com/