There's something called FreeSCI that is like ScummVM for Sierra's old graphic adventures, but I don't think there's an Amiga port. I do remember seeing a MorphOS port pop up on Aminet somewhat recently, though.
I've never heard of any user-level tools to create Scumm games.
And I also don't think any LucasArts games have been declared freely distributable, so you'll need to find somewhere to buy them. Flight of the Amazon Queen and Beneath a Steel Sky, 2 non-LucasArts games, have been released as freeware by their authors and you can get them from the
ScummVM homepage.
