A couple decades ago I ran an NSF-funded project to develop and run a public, open-source automated built-and-test platform for ~50 distinct versions of a dozen or so unix OSes (plus a token Windows version or two), long before modern CI platforms made this commonplace. We needed it for our own software and "productized" it for the wider scientific community. It was a ton of fun, and a beast. The diverse hardware in our test lab was like a zoo. Linux consolidated the industry and made the whole thing unnecessary shortly after I left.
