Cities: Skylines, everything that SimCity should have been.

Maximum Buildable Map Size: 36km² - 100km² (Mod): ✓
Full Modding Support: ✓
Map Editor: ✓
Asset Editor: ✓
Steam Workshop Integration: ✓
District & Policies: ✓
Offline Mode: ✓
Real Population: ✓
1,000,000 Agents: ✓
Working Traffic System: ✓
Power Lines & Water Pipes (SimCity 4 Style): ✓
Hydroelectric Power (Damns): ✓
Tsunami: ✓
Natural Resources: ✓
64-bit Game: ✓
OS - Linux, Windows, OS X: ✓
Under $30: ✓