It's a web framework. Directly, probably none. However there may well be plenty of sites/web servers using it.

It's funny because I've worked with ruby on rails my entire career and can barely see how he built the tool that such an open and inclusive community formed around. He was always an outlier in that setting and even more so now. My understanding is that he's not very involved with the project and even if he was it would be pointless to boycott it since he doesn't gain anything from it anymore. Hey and Basecamp on the other hand, yeah, neither are seeing a penny from me.

None on your PC.

Even in terms of the internet services that might possibly use it, it hasn't been fashionable in 15 years or so. Long standing services that started between mid 2000s and mid 2010s are the most likely things to use it.