You can download the 5.10version here:
> A LISP interpreter for DOS marketed by the Microsoft Corporation in the 1980's
I'm disappointed that it was for DOS. I'd have excepted a Lisp for Xenix ; )
tl,dr: an interpreter for MS-DOS and CP/M from the 1980s, no longer sold.
I've still got a copy of the DOS version of Microsoft MuMath on 5.25" floppies and the manual at my parent's house. Dunno if it's readable. I had a relative at Microsoft who sent me a few things I was interested in back in the 80's, including their C compiler.