What software translated PowerPC apps on Intel Macs?

Rosetta translated PowerPC applications so they could run on Intel-based Macs. Apple introduced it in 2006 as part of the PowerPC-to-Intel transition, beginning with Mac OS X Tiger 10.4.4.

The software worked as a compatibility layer that translated PowerPC instructions into Intel instructions, usually without requiring users to alter the application. It was based on technology from Transitive and operated largely behind the scenes, allowing many older programs to continue working after the hardware change.

Rosetta had limits: it supported many G3 and G4 applications but not every PowerPC-dependent feature, and it did not run classic Mac OS applications directly. Apple discontinued the original Rosetta in Mac OS X Lion 10.7 in 2011. Rosetta 2 is its later, differently targeted successor.