Probably his most influential projects have been ffmpeg and QEMU. Lots of people use software incorporating or derived from those, often without even realising

Probably his most influential projects have been ffmpeg and QEMU. Lots of people use software incorporating or derived from those, often without even realising. I think most developers would be proud of a legacy containing starting just one project like either of those. He's also got a great body of interesting other projects and hacks, including a linux capable VM running in the browser, a digital tv broadcaster using a single pin of vga, a popular embeddable javascript engine, a C compiler that could compile and boot the linux kernel in less than 15 seconds - allowing effectively 'boot from source', an award winning neural network based text compressor and many more - to say nothing of temporarily holding the record for most digits of PI calculated (using a formula he invented, and on a home PC).