Xerox PARC had Smalltalk, Mesa (later Mesa/Cedar) and Interlisp-D.
The platforms would first load the respective microcode into the CPU for the bytecodes used by the desired workstation environment.
Initially Xerox PARC made use of BCPL, but quickly they realised it wasn't the best way to write systems software and created Mesa to replace it.
After all, BCPL was intended to bootstrap CPL, not to write fully systems with it.
Other 60's computer companies were making use of either Algol or PL/I dialects, all the way up to the 80's.
Lots of juice papers at Bitsavers.
