http://www.meridian59.com/
Meridian59 is the first MMORPG, I beta tested in in '94 or '95 and it is a bit ugly to todays mega polygon user but it was fun. They OSS'd it recently and the source is available on the front page, there are two servers one for starter/social fun and one more for hard core pvp. I think I ran it on a 486 with a generic 1Mb vid card so it will surely race along on a N900.