Magic Engine, programmed by brothers David & Cédric Michel (chapeau pour votre grand émulateur) has been around for a while now. The first generation ran on MS-DOS, and I am proud to state that I registered it as soon as I became aware of it. It was around the time that other great emulators like Sparcade and Miha's C64 emulator was was ruling the emulator-universe. The first edition I came across already sported a 'rom-selection'-menu and it could work with a special combined hucard file generated by a german fellow especially meant for the Magic Engine emulator.
For years nobody could touch the accurateness of the emulator and I still regard it as one of the most compatible tg16 emulators out there. It is not open source and the sole persons responsible for its development are David et Michel! A windows version was developed, sporting directX or OpenGL hardware acceleration. I registered and used this emulator quite a bit - had great support for gamepads like the logitech rumblepad 2. There was a version out for OS8/9 that needed gamesprocket but I was not able to use that due to the fact that my Dutch OS8.x installation didn't come with the appropriate gamesprocket version and there was no way in hell to install another another language version for it. So I was deprived of a good Macintosh TG16 emulator for quite a long time. Things luckily changed when I got my G4 running OS9 UK but I never got around to running emulators on it untill quite recently when I wrote an retrogaming/emulation article on OSX Tiger a while back. Richard Bannister's TGEmu-port is quite good, but nothing beats the slick user interface and easily configurable controls of the Magic Engine emulator. It is true that TGEmu is a true OSX application and the whole interface of Magic Engine is just the same as the Windows version, slick and cool but not standard OS X menus although there is a menu bar at the top when the emulator doesn't run full speed.
Registering the emulator is just as easy as getting Richard's emulator enhancer, via paypal you only pay a small amount of money and you'll be sent a key file which is basically an encrypted text file containing your name and serial number amongst some pieces of code so that the emulator recognizes the registration properly. Just drag the key-file into the emulator folder - it functions like this on all versions be it DOS/Windows or OS8/9/X and the emulator is unlocked. It is possible to get a discount when you want to register both the Window and the OS X versions.
The OS X version I tested was MagicEngine v1.0.0 PR 10.4, and it runs on Tiger (10.4) and Leopard (10.5). I am not sure about Panther (10.3). It recognized my logitech rumblepad without any problems and I was able to define all keys appropriately. I did run into a little snag where the emulator wouldn't initialize properly after quite a bit of gameplay using the non-registered version, but that was quickly resolved by deleting the magic engine folder inside the application support folder. Probably some issue with corrupt settings, but that only happened once and has not returned.
On my 2.2Ghz Intel Mac it runs flawless, smooth in a window or full-screen. The sound is just amazing, very close to the original Tg16. CD-rom games are supported and I recommend this easy to use emulator to everyone who wants to give his/her original Tg16 cds a spin. Copied games do also run on the emulator - probably due to the fact that the Tg16 actually was the first console to sport a cd-rom extension in a time where copy protected cds were still largely unknown.

System requirements for the PC version:
v 1.0.x
* Windows 98/2000/XP
* Pentium III 600MHz
* 256 MB of RAM (512 MB recommended)
* GeForce 2 / Radeon 7500 or similar video card
* SB Live sound card

v 0.9.x
* Windows 98/NT/2000/XP
* Pentium II 400MHz
* 64 MB of RAM (128 MB recommended)
* TNT 2 / Voodoo 3 / Matrox G400 or similar video card
* SB 64/128 sound card

System requirements for the Macintosh version:
v 1.0.x
* Mac OS X Tiger 10.4.x
* PowerPC G4 800MHz or Intel Core Duo
* 512 MB of RAM
* GeForce 2 / ATI Radeon 7000 or similar video card

v 0.9.x
* Mac OS 8/9 or Mac OS X in Classic mode (CD emulation does not work in OS X)
* PowerPC G3 400MHz
* 64 MB of RAM (128 MB recommended)
* ATI Rage 128 video card

Conclusion: for a pre-release version (PR 10.4) this is one mighty fine emulator and there are a lot of x.0 version emulators out there that are more buggy than David's work.

Ratings on both the Windows & OSX versions:
graphics 5/5
sound 4/5
pricing 5/5

http://www.magicengine.com