Hello! as3sxfr is a free open source tool for generating sound effects, primarily for games but they could be used for anything you like! It's quite an old tool now though, why don't you give my new sound tool ChipTone a try?
All sounds created using as3sfxr are FREE to use for any purpose, commercial or otherwise, under the CC0 licence. However, if you'd like to, you can donate below!