- Laissez-Faire Economics: Non-military colony improvements build themselves according to a hidden preference system (eg "colony is tight for food, build a hydroponics farm for future pop growth", or "let's make money! Build a stock exchange!"). Even moderately high taxes (20%+ say) cause unhappiness and the like though.
- Capitalist Economics: More or less like MOO2, but colonies also build their own stuff in the background. So you can come along & order a new auto-factory, but the AI will keep building that hydroponics farm as this goes on. Moderate taxes are okay for this system.
- Socialist Economics: MOO2, with high taxes required: since you're building everything, private industry doesn't need the money to build it itself.
- Totalitarian Economics: For real micromanagement lovers. God only knows how this would work vs Socialist Economics though .
There could also be other benefits / penalties: for example, a laissez-faire economy will happily accept hard-working immigrants (eg 19th Century USA), but also be more open to enemy spies, tech theft missions etc. Population and economic growth will probably also be higher, on the basis that people are doing their own thing and don't care much what their government (ie you) say. However, a laissez-faire economy is not good in a war (no money for warships), and people will get unhappy in a dictatorship because they're used to so much freedom. It'll do great as a peace-making faction though (money > war), a trading faction, and in the very end game its economic output will let it handle wars well due to sheer economic growth. Assuming it survives to the end game, of course.