Sweet16 is the most capable Apple IIgs emulator for computers running OS X. Based on the BeOS version of Sweet16, which was in turn based on the outlandishly popular Bernie ][ The Rescue, its code is mature and positioned to have more and better features added over time. Apple IIgs fanatics and nostalgic '80s junkies alike will love Sweet16!
Note: While the software is classified as freeware, it is actually donationware. Please consider making a donation to help support development.