A while back I downloaded the Conspiracies Deluxe mod for OFP. If I remember right it was sort of a STALKERish inspired mod for OFP that was released before the actual STALKER game was out.
Decent enough little mod that tries to do something different. I really liked the atmosphere in a lot of the levels early on. After the 20th or so level I ran into more bugs and got lost more than in the earlier ones so resorted to some endmission cheats to get past that. It had a nice mix of troop combat and then zombie combat.
Even though OFP is old I still like how it looks for some strange reason. Still amazed by the amount of mods and activity it still has. It really makes me want to try my own mod, at least mission wise, building something postapoc. I also tried some Chernobyl mod but it didn't have any missions at the time (At least that is what I recall). Sort of makes more sense to just replay STALKER but there is something about OFP (and also ArmA) that draw me back.
The author's website is here. Filefront currently still has a link to the mod up here.