Closer to MOP
Closer to MOP is a compatibility layer that rectifies many of the absent or incorrect MOP features as detected by MOP Feature Tests. Closer to MOP has an asdf system definition, so it should be straightforward to include it in your own projects. The package that exports the relevant symbols is called CLOSER-MOP and also has the shorter nickname C2MOP.

Closer to MOP is written and maintained by Pascal Costanza. See Common-Lisp.net for more information.

CLOS MIT