Today marks 3 months since I started working on my secret project. I have kept it a secret for a long time now, but I am reveiling details of what I've been doing. http://dgrove.blogspot.com/ -- I have written an article about it there (March 15). Basically, this engine will be programmable by programmers, and designable by non-programmers. It's an engine for EVERYONE. All written in C and will emulate the original engine 100% perfectly. Also, I have many more screen shots in the March 18th post on the blog! One of them shows another picture of a game running, and the rest show the utilities that will be supplied with the engine. And I have an FAQ on it here.

I'm curious what libraries you are using.

I am using two libraries to assist me: Allegro and AllegroOgg.

That's right, and you can make Sonic games that play and feel exactly like the originals because my engine is based on the same algorithms that make players jump, run, go around a loop-de-loop, etc. I've got many algorithms calculated down to exact replicated numbers as the original games. So I'm basically rebuilding the original engine, and I'm giving it more features and abbilities to make more advanced games that still play and feel like the originals.