[Tool] Does an Engine-like program exist, or something similar?

Hello, I'm new to all of this but is there an "engine"-like program that has stuff pre-put in it already that you can build from? Like you can build your own region within this program that has assets & such already in it, and you can add more to it from outside downloads.

Sorry if that doesn't make total sense, its kinda hard for me to explain, but if something like that doesn't exist, I'd appreciate it if you can at least point me in the direction of tools that allow me to build my own region from scratch or from a rom hack. I would like to do at least a gen 3 era style game. Also, sorry if this gets asked a lot or might be inappropriate, I'm just lost haha.

I tried looking around on the site but couldn't find exactly what I had in mind or I didn't understand.

Thank you!

The CFRU doesn't let you build an entire game from scratch, but it does provide you with many features that could help you make a hack.