Half-Life is approaching 25 years old. While that means it certainly looks dated compared to new releases, it does mean that it’s becoming easier to play Half-Life in unexpected situations. The whole game is just 700 MB, after all, which is basically the amount of data you’d expect from streaming a full-length video.
In fact, one Half-Life fan decided that since there’s no need to install the game on your computer anymore he was just going to make a web-based version that’s playable through your browser. Dash (@x8BitRain) over on Twitter used the Xash3D engine to create a browser-based version of Half-Life that you can play right now over on GitHub.
For those unaware, Xash3D open-source 3D game engine that was made specifically to be compatible with GoldSource games and mods. As noted on the ModDB site, it was "built from a scratch," and "overcomes obsolete GoldSource engine's limits" to make it easier for mod makers to create Half-Life mods. Or in this case, to just throw the entire game onto a GitHub repository and make it playable through our browser.
Head to Dash's site and you'll be presented with three options. Hazard Course loads Half-Life’s tutorial, while HLDM is for a Half-Life multiplayer death match. HLDM doesn't seem to work right unless you enter it through the console, and since there's no multiplayer support, there's no reason to select this option.
The option you want for a real game of Half-Life is Uplink. This brings you the original Half-Life experience starting at around Chapter 5 from the original game (that's when Gordon and the gang realize the military is trying to kill everyone to keep the interdimensional incident from getting any worse). The sound is absolutely awful and the game will seemingly freeze if you die or have a loading screen, but just stick with it and it'll fix itself. Also, don't alt-tab away otherwise you might lose your mouse tracking.
Dash acknowledges the build is a little buggy as Xash3D uses a 2017 codebase, which apparently was a time period where "proper browser integrations" hadn't been done yet. He calls it more a "curiosity" than anything definitive, but a few programmers have reached out with suggestions for improvements, so perhaps a new version might arive with the full Half-Life experience and better sound fidelity.