GSC Game World is apparently working on a new S.T.A.L.K.E.R. add-on called S.T.A.L.K.E.R.: Call of Pripyat as well as a full-fledged sequel to their irradiated first-person shooter. This is according to rough English translations on ClanBase and the TTLG Forums of comments made in a Russian-language chat with GSC Game World's Sergey Grigorovitch. A question asking if the April "Call of Pripyat" entry on S.T.A.L.K.E.R. calendar was an April Fools' joke was answered with the revelation that this is the name of a S.T.A.L.K.E.R. add-on that they expect to release this autumn. He also apparently says they are working on S.T.A.L.K.E.R. 2. Thanks Kincaid.