Mops
Like Yerk, Mops is descended from the ex-commercial object-oriented language Neon. It was developed by Michael Hore <mikeh@kralizec.zeta.org.au>. Mops features an optimising native-code compiler; it is much faster than Yerk, but less compatible with Neon. Mops includes extensions such as multiple inheritance.
Version 2.3.1 includes a compiler, documentation and an editor.
A Macintosh version is available. ftp://oddjob.uchicago.edu/pub/Yerk.