So something that is a somewhat common assumption is that ROM hacks are straight illegal which isn't true. As a matter of fact the only factor that can make them truly illegal is if anyone tries to seek a profit or sell the content that has the original creator's IP's and trademark characters embed.
So ROM hacks in a way are the internet's baby because there is genuine passion being fed into these projects and the fact of the matter is that they're criminally underappreciated. So users have gone so far as to remove almost any trace of the original game's identity and created their own with the same system to provide a whole other title of that age old system for the people who want to experience new and different things just the way things used to be.
Now it is widely understood that obtaining copy's of video game ROMs or ISO images etc is strictly illegal and violates copyright law. But if anyone who owns a copy of the original games and has flashed them to their computer so that they can have backups in case the cartridge breaks can edit their ROMs and share it.
This package includes about 30 different ROM editors designed especially for Pokemon game ROMs now the supported ROMs are not included within these products or within this package you have to obtain that via flashing your old games onto your PC.
These sources and others can also be found at THIS URL