Make a Game of Life simulator

A battery without the use of BTRY? If you are wondering how, make a loop of conductive solid(s). By the way, @FeynmanLogomaker , your avatar is annoying. XD

Make a TNT factory that will make TNT blocks without using TNT directly.

how about a

Laser

Reactor

City

Factory

Space Ship

Counter

Computer

Calculator

A bursting Dam simulation

Rocket motor

Internal cumbustion engine

hot steam cannon

fireworks display..........

I could keep going.

Planet with lots of features like volcanos and unstable core and cities with working satallites and stuff

I would say a city but...there are too many city maybe something like a under water cave/layer. 

You could make a city if you have some really cool buildings that are very detailed, but I would recomend you build a city underground under a forrest or something; it would make the city more interesting :D