This predates the WebAudio API, and so it builds data URLs as WAVs instead. Every sound can be represented as a short string, and the tool can be used as a library that procedurally generates the sounds from the strings. It also has a "song mode" where notes can be provided to guide the sound, which makes certain types of more complicated sounds possible to make, including jingles and short songs.
It's definitely dated now, but if anyone is interested, you can find it here
https://www.leshylabs.com/apps/sfMaker/
See the "Example Sounds" at the bottom of the page to hear what it can do.