It's open for any one of us to join and completely voluntary. I worked on my private open source project that has nothing to do with my company on one of the hackethons. Since we host the hackethon in the weekend the costs of it are really low. Just the place, and some provisions. I work at a really small company of 5 people. We discuss everything with the entire staff. We have a monthly knowledge sharing session where we do mob programming for fun. We develop a small application just to learn how we each have a different development style. Loads of fun and very educational.

It doesn't sound like his are company-related.

My company takes a reasonable approach to this I think. The hackathon itself takes place Thursday and Friday, so it happens on work days. But the judging takes place Monday, so there's an obvious opportunity to continue to work over the weekend. No one has ever mentioned it though.

Also the whole C-suite takes part in the judging so it really is an opportunity to show off your work.