I made a web-based clone as a Java applet circa 2003-2004 for a $300 contract on rentacoder.com for which I was never paid. :)
I built just the basic skeleton of a game engine, and stupidly handed over the code to the client before they paid me. They went on to find another contractor to dupe and turned it into a game called "Fat Super Heroes" which was online for a while on some sleazy website where you could gamble real money on the outcome of the game.
The original (horrible, terrible, hacky) engine I wrote is here:
I don't think it ever got much real popularity; I was not a fan of the theme and the second contractor added a bunch of bloat that made it load slowly, etc. But it was quite a fun learning experience.
Pretty cool. There was also a playable web version of Hedgewars via emscripten at some point. The emscripten version is currently unmaintained, and I think the project would be happy for someone to upgrade the toolchain and provide patches that make it work again. Check them out at https://www.hedgewars.org/ and #hedgewars @ irc.freenode.net
You could even turn websites themselves into arenas to battle in. :) Imagine blowing up a hacker news comment.