Slashstone SoundFX Builder is a small sound generator utility i wrote around 2005 while making Nikwi for the game's sound effects. It is largely inspired by an old program i found on some shareware collection CDs, though sadly i do not remember the name anymore.
The program is very simple: you drag around points in two main windows to create an envelope for frequency and volume and adjust some "knobs" for additional filtering and that is about it. The sound can be exported then as a WAV file. The effects are really primitive sounding and i mainly uploaded this tool because it was the "missing piece" for Nikwi's code over the years.
The tool was written in Free Pascal and Lazarus with a tiny part in C to play back the sound buffer via SDL. I fixed a couple of bugs and compiled it with a recent version of Lazarus/FPC so it should work fine, though i didn't bother updating the SDL and playbuffer DLLs (but they work anyway, that is Windows for you).
You can download version 1.1 from here (1.1MB). The archive contains the Windows executables, a few examples, source code (licensed under MIT), the C code for the DLL for sound playback as well as a small library for loading SSFX files directly (this was also included in Nikwi's source code).
Some example sounds: birdwhistle.wav (9.51KB) blipblop.wav (25.8KB) fall.wav (64.6KB) jump.wav (10.8KB)