Not sure how many folks here enjoy the massively multi-player online role playing games, but there is a free game that y'all might enjoy. It is based on 15th-18th century seafaring and crafts and called 'Voyage Century.' You can find it here: http://www.voyagecenturyonline.com
If that is not your style, you can always check out the RPG's here:
http://www.bittorrent.com/search?category=Games&genre=MMORPG
You will find games based on the 'Continent of MU' and 'Rune Scape' titles as well as martial arts and medieval fantasy rpg's.