Here you find all sorts of browser-based Sonic the Hedgehog utilities. Do note that these require HTML5.
To start, pick a tool: (these open in a new window)
Decompressors (WIP/Alpha)
Sonic 1 Title Card Generator (Beta)
Soni's Sonic Utilities Copyright (C) 2015 Soni L. (SoniEx2) MIT license. Source Code.