The dystopian gumshoe's cases Mean Streets and Martian Memorandum can be added permanently to a free GOG account for absolutely "zip, zero, zilch, nada" until December 24. Those who already own the pair can register for "an alternative gift."
The other games in Access Software's adventure series--Under a Killing Moon, The Pandora Directive and Tex Murphy: Overseer--are on sale at GOG for $9.99 each.
The gift is apparently only the first holiday surprise from GOG, who tease "more exciting, jaw-dropping news!" will come in the next few days. Thanks to Taczbr for the tip.