The 1995 real-time strategy game, rebuilt from the source code Electronic Arts released under the GPL and running in your browser.
About 65 MB, downloaded once and kept in this browser, with the music. The movies are not included; add them from your own disc image with the link under the game.
EA released C&C Gold as freeware in 2007. The GDI disc image (CNC95_GDI.iso) contains everything, movies included.