FreeRealms is a site where you must download it but it is totally free.
meez
Yes second life
Xivio.com is great! Its a 3D no download free virtual world!!!
WebkinzMeezThere.com
not really, but if you have an HP computer go to the game section and type Virtual families. you can play for 4 times free and no downloading! try it!
free trial??
free trial??
nowear
Animal Jam, another free world, unless you get a special membership.
runescape
I think there is no way whatsoever.
no