Unfortunately I haven't found one. But I have found some recent posts The first is from Bryan Alexander who comments on the evolution of virtual worlds at his blog http://infocult.typepad.com/infocult/2007/02/towards_third_l.html
He mentions four alternatives that I want to explore further this week.
Multiverse, Ogoglio. Outback Online, Croquet
Also, sharing a post from Onder Skall Dated March 2007
Onder Blogs at Second Life Games where he provides a easily digestible overview of the games people play in second life. Well worth a browse.
http://www.secondlifeherald.com/slh/2007/03/alternatives_to.html
He compares a number of virtual worlds based on the criteria below
HiPiHi
Entropia Universe
Areae Inc.
Outback Online
The Sims online
There
Active Worlds
Weblo
Project DarkStar
Virtual Object System
1. Cash transactions must be easy and readily accommodated flowing both into and out from the system.
2. Users must be able to create unique content and retain some form of ownership over it.
3. The fabric of the world itself must be possible to affect. IE: land ownership, room decoration, or some other content that remains viable even when the player who created it is logged off. (”Pervasive” is the word I’m groping for here…)