But rimworld is not a defense tower...

I would say that its a mash of various other games and not at all like Rimworld or Prison Architect.
It has similar building mechanics to Oxygen Not Included, the constantly changing resource potentials of Roaming Village, with a bit of Stardew Valley, and of course, a tower defense game similar to something like Plants vs Zombies

Originally posted by Greystar:

It says new type of game, colony sim + tower defense... That's Rimworld in a nutshell.

i don't remember being able to move your base through the world shooting at enemies in rimworld.
or being able to dig down.

this is about as much a rimworld clone as minecraft is a doom clone. both are first-person 3d survival games with blocky, pixelated graphics and monsters as enemies.