The new Tempest Rising update makes the superb, Command and Conquer inspired RTS better via new maps, multiplayer modes, and a big discount.

Renegade and Generals, however, call for a whole lot more nostalgia: STLport 4.5.3, the SafeDisk API, the GameSpy SDK, the RAD Miles Sound System SDK, and at least eight more.

The games in question are Command & Conquer (aka, Tiberian Dawn), C&C Red Alert, C&C Renegade, and C&C Generals + Zero Hour, all released under the General Public Licence.