I have surveyed the field of ABM simulation software,
and have finally decided I will either settle for Repast or
Mason -  both appeal to me: Repast because it is specifically
designed to meet Social Simulation needs and seems to has
a big following in the socsim community, and Mason because of it's
design (on the code level). (lean and mean  ;-) 

Has anybody tested both platforms and can offer some insight
on the differences (I'm interested in _opinions_ :-))?

I would need it to model cultural diffusion processes, my approach
stems from viewing human societies as complex adaptive systems
and special interest will be invested in modeling the cultural processes
(either with cognitive agents, or "memetic" data structures or  something
in that direction).

A good starting point seems to me the sugarscape model (I also want
to include resources and competition between the agents).
The agents should be adaptive in the long run (read: learning ability) -
although this goes somewhat contrary to the keep it simple paradigm.

There is an implementation for Repast, it is also listed on the Mason site
as a project but I did not find a download.

Basically, what I'm interested in is a very stable platform with an open
community, and an ease of integrating other technologies (for instance
BDI with Jason)

Best Regards,