Massively multiplayer online games aren't just for RPGers. Hardcore simulation games were among the first to adopt the massively multiplayer model, and there has been a steady increase in the number of games offering first-person shooter elements in recent years. The games below, unlike most RPGs, all feature combat systems that require a steady aim and fast reflexes.
Futuristic vehicular warfare with hundreds of players is what SOE achieves with PlanetSide, and it does offer action on a scale that is truly impressive. Your character is persistent, and you get access to more weapons and vehicles as you increase your Battle Rank, but the game is really about heavy-duty firefights. Highly recommended for FPS fans.
Formerly known as WWII Online, this is a first-person online battlefield simulation that is played on a terrain modeled one half scale map of Europe. Players command and crew a variety of vehicles and aircraft or fight as foot soldiers. An excellent title for hardcore simulation gamers that don't mind the steep learning curve and want a much more realistic and demanding game experience. A joystick is essential for playing anything other than infantry.
Jumpgate is a massively multiplayer space combat game which features 3 playable factions, 48 ships in 16 different hull classifications to fly, and over 130 sectors to explore. The graphics are getting dated, but it has a solid flight model, unique player vs. player gameplay, and sheer value that set it apart from other MMOGs.
Warbirds is massively multiplayer flight sim which lets you take to the skies in a variety of World War II aircraft. There are no roleplaying elements, but you will need to hone your pilot skills to survive in this highly competitive online dogfight. Although this is a challenging game for beginners, you'll find the community of players as warm and helpful as they get.