The S.T.A.L.K.E.R. franchise takes place in Chernobyl after the second disaster, called 'The Zone'.
S.T.A.L.K.E.R.: Shadow of Chernobyl
S.T.A.L.K.E.R.: Shadow of Chernobyl takes place in 2012, 6 years after the second explosion. You play as the character called "Marked One" who has amnesia and must find out about his past as well as doing objectives for various people. Contains similar gameplay of a non-linear Role-Playing with Artificial Life. The game is known for its strong mod community, the major ones being Oblivion Lost and AMK, both of which add content and remove glitches.
S.T.A.L.K.E.R.: Clear Sky
S.T.A.L.K.E.R.: Clear Sky is a prequel to the original game which is one year before the story of the "Marked One". The player takes the role of Scar, a mercenary who is after Strelok. The game features Faction Wars and improved graphics, but just as many glitches.
S.T.A.L.K.E.R.: Call of Pripyat
S.T.A.L.K.E.R.: Call of Pripyat (or CoP) is the third game in the S.T.A.L.K.E.R. series. It follows where Shadow of Chernobyl left off, only this time putting you in the shoes of a new character. You play as Major Degtyarev, an agent sent in by the military. Your goal is to blend in with the other stalkers as you try to find out what happened to a squad of men who's helicopters had crashed in the Zone. Call of Pripyat features the same core gameplay as the previous games, but adds some welcomed additions. CoP refines the UI/HUD of the previous games to make it more managable and less tedious, as well as updating the look and feel of it. There are now "safe zones" which are areas where violence is not allowed (you're forced to holster your weapon before you enter) and acts as a quest hub. Located in the safe zones are traders, weapon upgraders/repairers, major NPCs (quest givers, etc.), your own personal stash to store items that you find, and a bed to sleep in. Other new additions include: Three new areas (Zaton, Jupiter, and Pripyat), new mutants, new enemy AI, improved graphics, improved quests, drugs (medical), a new storyline, new NPCs, and more. It should also be noted that the S.T.A.L.K.E.R. games are known to be extremely buggy, but Pripyat is definitely a major improvement in terms of polish/bugs.
S.T.A.L.K.E.R. Online is an MMOFPS set in the S.T.A.L.K.E.R. universe. It is currently in open beta with both an English and Russian client available. http://szone-online.net/
Note that this game is in no way related to GSC Gameworld and is not part of the S.T.A.L.K.E.R. franchise.
S.T.A.L.K.E.R. 2 is currently in production for the PC, Xbox360, and PS3. Not much as been released in the way of content, and there has been rumors of cancellation. GSC still insists through their twitter that it is still in production, and is slated for release in 2012.https://twitter.com/#!/gscstalker
Later on April 25th, 2012. S.T.A.L.K.E.R. 2 was confirmed to have been cancelled by GSC.
Books & TV Show
Inspired by 1972 book Roadside Picnic, referencing the stalker occupation which illegally scavenges 'The Zone'.
Since 2007, there have been over 45 books (in Russian, English, & German languages) published in the S.T.A.L.K.E.R. series. The aggregate sale for the books have topped 5 million and it has been the #1 sci-fi series in Russia for the last two and half years. The English books are considered in cannon with the rest of the universe.
On Nov. 10, 2010, GSC released a trailer for the S.T.A.L.K.E.R. TV show. The shows official website is http://www.kinostalker.com/
The Stalker community is well-known for its many mods that tweak and optimize the default games. The most popular series of mods are the STALKER Complete series that drastically improve the graphical quality and fix many of the bugs.