The "Sonic 3 Complete" or "wsonic3.bin" hack is a modification of the Sonic & Knuckles ROM that aims to recreate the original Sonic 3 game that was scrapped and reworked into Sonic & Knuckles. This hack combines elements from the cancelled Sonic 3 game with gameplay mechanics from Sonic & Knuckles.
The for editing Sega Genesis games (like Hivebrain's Disassembly). Tutorials on how to use a Hex Editor for basic game tweaks. The checksum values to verify if your file is legitimate. Sonic Knuckles Wsonic3.bin File Download
For assembling a final .gen or .md ROM file after making modifications. The "Sonic 3 Complete" or "wsonic3
Some emulators require a specific checksum or header. Try: Tutorials on how to use a Hex Editor for basic game tweaks
That being said, here's some background information on the topic:
Are you interested in learning more about Sonic & Knuckles, its development, or other ROM hacks? I'd be happy to help.
Downloading standalone .bin files from the original game is legally considered a gray area or direct infringement if you do not own the original cartridge.