I did a PoC in college (~2008!) where I coded a distributed rainbow table generator in JS. It'd assign a block of hashes which would get sent back to the server. We showed that a single webserver distributing the work in a naive js implementation (long before webworks and wasm) could outpace a fairly decent local c impl (we were undergrads, so definitely not optimization experts).

Was fun until sites actually got on board with salting.