pucrunch forms the basis of the de-facto standard for compression on TI-68k calculators, ttpack (PPG). And it's LGPL'ed.
For best performance, write the decompression routine in ASM. Samuel Stearley did two versions of the decompression routine in 68000 assembly: the fast one is around 80 KB/sec and between 500 and 600 bytes, and the small one is <~30 KB/sec and between 200 and 300 bytes.