The ones that I know of are (not counting the numerous forks of Damizean's movement engine people have made):
* Damizean's very old GM6 "green" engine with those green cyberspace test tiles - as far as I know, this was the first fully functional 360 degree movement engine for Game Maker, and while amazing for its time, it was made years before Mercury published the Sonic Physics Guide and it definitely does feel a little off. But could it be modified for accuracy without giving it a major overhaul?
* Damizean's examples pack - this was a slightly newer one that had plain black test tiles. From what I could tell it felt pretty accurate and a lot of people used it
* Damizean's Xmas Engine/Sonic Dash/Sonic Dash+ - some time in 2007 or 2008, Damizean's released what was commonly referred to as the "Xmas Engine" and movement-wise it felt great. If I recall correctly, the Sonic Dash engines are forks of the Xmas Engine, though I don't recall if they made any changes to the physics. I do know that the original release was still years before the Sonic Physics guide was published. The organization of code in this engine is a mess, however.
* AeroGP's unamed Game Maker Studio engine - this is a very recent engine and from what I remember testing it, it felt great, and was definitely made after the Sonic Physics guide was published. I do recall some comments in the thread about some very minor differences in slope physics, but are they really a huge deal?
* Sonic MAX Engine - as far as I know this is 100% accurate, but the documentation is poor and its on GM:Studio so you have to deal with slow compile times.
How important is it to have 100% accuracy to the Genesis/Mega Drive titles in a Sonic game? Because even as far back as Damizean's examples pack, while not 100% accurate, is still miles ahead of Dimps's Sonic 4 engine. Another issue I have with these newer engines is that there's too much implemented (I know that sounds ridiculous), I would really just like plain-movement versions (I like to implement things my own way). Of course, then you could say why don't use you use the one from Damizean's examples pack, but I recall that one did things differently than what the Sonic Physics Guide says. I've started my own movement engine using the guide as a reference (which is a lot easier for me to understand now rather than in 2010 now that I understand trigonometry and calculus), but I'm wondering is it worth doing so with all these other engines out there?