Have You Played? is an endless stream of game retrospectives. One a day, every day of the year, perhaps for all time.
Remember that time Valve made a cover version of another developer's game?
Operating with the thought that imitation is the sincerest form of flattery, Deathmatch Classic is a "tribute to the work of id software". Specifically, it's a recreation of Quake 1's deathmatch in the Half-Life 1 engine, mimicking its shotgun, rocket launcher, quad damage, level design and physics and so on.
Interestingly, it's not very good. The Half-Life 1 engine - retrospectively called GoldSrc - was built upon the Quake 1 engine, but with enough changes to its character movement, lighting and so on that it feels distinct. Deathmatch Classic doesn't wind back those changes so much as seem to build a Quake 1 impression on top of them, and it doesn't feel quite right. Maybe it's the way the gun bobs, or maybe it's just that I generally prefer originals to cover versions.
Deathmatch Classic was originally a free mod for Half-Life, but you can now buy it separately for £4. Steam reviews suggest there is maybe only one lost soul still playing it.