Counter Strike: Global Offensive

Counter-Strike has been the most popular multiplayer game since it evolved into a standalone game from a Half-life mod in year 2000. Since then we have seen many new updates and sequels including the popular CS 1.6 and CS: Source. The latest Counter-Strike is called "Global Offensive" and it's official is release expected this year. In the meantime you can enjoy the Global Offensive BETA version which has recently leaked into public.

Note that even though this is a beta version it has proven to be quite stable.
Like the previous CS releases, it has an integrated bot system which you can use to create AI opponents to play against. You can also create online & LAN servers to play with your friends or join one of the existing public servers.