Tier 0

Tier 0 is your starting base. It continuously spawns zealots for you to fight with.

Chronoboost
Regardless of tier your base can cast a chronoboost on itself to produce units faster or on your defensive cannon to make it upgrade/attack faster.

Upgrading
Your base can upgrade into one of three races: Protoss, Zerg, or Terran. All three upgrades are the same price and are available about 8 minutes and 50 seconds into the game.