Half-Life, online, in the browser! Made possible due to Xash3D, a compatible 3D engine that's been ported to WebAssembly. Firefox apparently works best, but I kept running into "gaming in the browser" problems such as shortcut conflicts and fullscreen glitches. The right game, in the wrong place, can make all the difference to a Wednesday morning…
Be sure to select the 'Uplink' pack, as the default "HLDL" pack won't launch a single-player game.