If you liked the classic Ogame before all the p2w stuff was added, you'll like this game.
OGame - OGame is an addictive, Massively Multiplayer Online, Real-time Strategy, Space-war, and Money Management Browser-based video game develop by Gameforge AG.
Galaxy on Fire - Galaxy on Fire is a space combat and trading simulation.
Xterium (War of Alliance) - Xterium (War of Alliance) is a strategic space simulator in real time. Fight with thousands of players around the world at the same time to become the best. To do this you will need a regular browser. Learn how to manage a Space Empire!
Cloneuniverse - You start with your first planet in a big galaxy and expand your empire with more and more planets. At the same time you have to defend yourself against other players, form alliances. All around a nice game and what is most important. No Pay to Win
Entropia Universe - Entropia Universe is an Addictive game for those players who love playing MMOFPS games.
Gratuitous Space Battles - Gratuitous Space Battles is an Adventure-based, Real-time Strategy and Single-player video game developed by Positech Games.