Basilisk II is an open-source 68k Macintosh emulator which can run versions of Mac OS prior to those supported by SheepShaver (i.e., System 7.5.3 and earlier).
A wiki-based tutorial provides guidance on how to set up the emulated system. Once the basics are set up, you can configure even more features (e.g. printing and AppleTalk) depending on your needs and/or rabid fanboy desires. Since I just wanted to run a couple of simple games I can't speak about those features, but I found setting up the basics quite difficult, even with all the required files.
However, once set up the system runs just like the original - except for being blindingly fast. The whole emulated system loads on my computer in a matter of one or two seconds, which, one can conclude, if history is an accurate indicator, is how fast modern systems would load on standard computers about fifteen years from today.
Sam's Protip: If you find, like me, that you can't seem to get Basilisk II working no matter what you grind through its gears, you might try out Edward Mendelson's "WPMac 68K Appliance", which provides a download that should be ready to run.
Pros
- Runs extraordinarily fast and well
- Permits access to other files on your hard drive
Cons
- Quite difficult to set up
- If you own the necessary files for setting up from scratch, they are probably on deprecated media (i.e. floppy disks)