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Quake-like game made with JavaScript takes up just 13KB of storage
(www.tomshardware.com)
This is a most excellent place for technology news and articles.
And I was blown away the ps1 game Vagrant Story turned Into 90mb file as a chd.
That said one of the games I enjoyed most even when I had an Amiga was a 48k ZX Spectrum game called Chaos.