Here's a blast from the past. The original Galcon came to the Play Store when it wasn't even the Play Store - back in 2010 it was still going by the name "Android Market." It was a super-simple strategy game, adapted from an almost ancient PC shareware title called Galactic Conquest. The original mobile game was quite a popular one - sort of a Threes for the real-time strategy crowd - and today the very welcome sequel has arrived on Android.
Galcon 2 follows the dirt-simple formula of the original. Your base continually builds ships, which you can send out to capture planets with a set value. Captured planets will then build even more ships, which can be sent to capture more planets, rinse and repeat. Things get interesting when you reach an opponent: planets gain defensive strength as they build up ships, and you'll have to send (and destroy) more ships to an enemy planet than they have saved up in order to capture it. The enemy will be doing the same to you concurrently. Since ships are both the game's resources and its units, combining the two traditional pillars of strategy games into one, Galcon becomes almost purely about timing, positioning, and logic.
The updated version of Galcon includes integration with Galcon.com. That allows players to play on a galactic map with conquest on a massive scale. There's also a guild system that facilitates some impressive multiplayer battles, creating games with an impressive amount of fast-paced tactics and strategy. The game is free, accounts for the multiplayer portion can be made anonymously.