I discovered today that my most played game on Steam is Astronner with about 500 hours, and my second most played is Surviving Mars with about 500 hours.
Continuum. I have more than 10 thousand hours on my main account, 3 thousand more on alts I do not have access anymore. Most of the time was afk or just being online since it had a chat and very lightweight. You can see top players by usage time on the trenchwars server website.