Years ago I built a website in Factor for testing HTML 5 video in browsers using the Theora codec. It allowed uploading videos, playing them in the browser, converting to Theora, transcoding YouTube videos, etc. It operated for a few years.
About the same time I wrote an 8080 emulator in Factor and emulated Space Invaders and a couple of other games using the Factor UI code.
For quite a while it was my go-to language for implementing things.