http://www.planetarion.com/ Dunno if anyone's played it here but its a fairly fun/simple game. Sign ups for the new round start today and the round starts at the end of october. i'm sure there are other games like it, it just happens to be the one i found.
basically you build ships and steal other peoples asteroids and try to defend your planet and your galaxy (and your alliance if you make/join one) there is a research progression tree and you construct buildings to help you mine resources from asteroids, scan other planets, build ships, etc.
its entirely browser based and run off a tick system (1/hr). its switched to a mainly free game (paid by ads). you can upgrade your account but it seems the advantages are minimal (removes ads and small, one time resource type bonus)
i have no affiliation to this game and dont get anything if people decide to sign up play, just passing it along bcs it can be fun to play. its been round for at least 8 years and i've probably played 3-4 rounds in that time span (they're on round 29 now)
the playerbase is largely europian and players from gmt-5+ timezones (ie US and canada) will have a slight advantage bcs attacks typically start to show up around 10-11 pm est (to try to catch euros sleeping)