ScrumbleShip is described as 'is the most accurate space combat simulation devised to date. Gather resources, construct a capital ship out of individual blocks, then pilot it with AI or real-human help against other players'. There are more than 10 games similar to ScrumbleShip for a variety of platforms, including Windows, Linux, Steam, Mac and iPad. The best alternative is Empyrion. It's not free, so if you're looking for a free alternative, you could try OGame or SpaceHunt Game. Other ScrumbleShip like games are Avorion (Paid), StarMade (Freemium), Shores of Hazeron (Paid) and Xterium (War of Alliance) (Free).
Avorion is a procedural co-op space sandbox where players can build their own space ships out of dynamically scalable blocks. Fight epic space battles, explore, mine, trade, wage wars and build your own empire to save your galaxy from being torn apart by an unknown enemy.
OGame is a strategy-game set in space. Thousands of players across the world compete at the same time. In order to play you only need a web browser. Start out with a small planet and develop this into the hub of an interstellar empire.
SpaceHunt is a chat-based multiplayer adventure similar to Ogame and StarCraft: build a base and go on missions to explore the universe and attack other planets to gather resources and dominate the Universe.
Unscripted, living and thriving universe. First person action from the ground to the stars and beyond. You is always yourself, scavenging your first fruit from the tree or standing on the bridge of your flagship.
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!.
Bitfighter is a fast-paced team-based outer-space multi-player combat game. There are many game modes and unique maps. Players can (and do) create maps by using the built-in map editor. Space exploration for warfare, construction, and beyond! It's fast, fun, and frenetic.