yeah there is an mmo based on the stalker concept.
http://forum.stalker-online.so/viewtopic.php?f=38&t=4453&lng=en its in pre beta atm. but you can try what they have done so far. to be honest im not to sure about this, they seem to want a free to play game but ask you to pay in real euro's for equipment that can randomly fall out of your backpack... HMMM!!!... i suppose you can turn round and pick it up but more likely you will end up with a hole in the backpack that everything you own falls out of so your basically throwing money away... or so it seems.
http://survarium.com/en/ is also claiming to be the stalker mmo. this is the more likely official release but there is little real info on it...