CarbonLib is Apple Computer's device for helping programmers make compatible binaries between Mac OS 8, 9 and Mac OS X. When programmers "carbonize" their progs, their programs can run natively inside OS X or 9 (and sometimes 8).

CarbonLib is technically a OS 8/9 system extension which is loaded at boot time. CarbonLib a library of APIs. Mac users (including me) have found that with every successive CarbonLib release, stability, speed, and a handful of bugs get fixed.

CarbonLib 1.4 was just released today, and seems fine to me.