Updated Update! Version 1.02 is now available at the link below. I strongly urge you to download the new version, as it fixes a major bug that caused work to be lost when using Enigma compression.
Here's a little something I threw together in about 3 days: Sonic 1 Special Stage Editor, a programme that does just what its name suggests.
I needed something like this for a hack I'm making, and I thought it would be a fun challenge to throw an editor together quickly. I even gave it pretty robust Undo/Redo features, etc.