there is second life health, and there are player made combat systems and weapons, there was alot of stargate roleplays on it before with missions and sutch, but it have kinda gone down atm.
To download second life you go to
http://secondlife.com
and make an account then and download the client,
when you are on sl, you can open up the search or the map and type in Eternal calm, Eternal Calm is one of the main stargate sims owned by the gate builders.
A sim is a simulator a server the have a pice of vitual land on it,
the servers are owned by linden lab.
sl also have it's owne money L$, real money that have been converted over to micro Linden dollar,
you can earn and sell on sl.
I'm on sl to build and script and exsplore useing the stargate.
How the stargate system works on sl:
There are diferent sims (simulators ) on sl, the world is made up of them,
the world is built by players and linden labs.
A sim can be though of like a planet couse the stargates takes you from one sim to another by dailing the adress of that gate or the gate name, works like the real stargate needing a powersource to hold the gate open for a long period of time and so on.
Idunno if any of that made any sence o.O but it's better if ya try it I guess