From personal experience Cromix was written in 6502 assembly language. The comments were all in C but personal computers were not fast enough to run a C OS in 1

From personal experience Cromix was written in 6502 assembly language. The comments were all in C but personal computers were not fast enough to run a C OS in 1979. I doubt it was licensed since they reverse engineered the API (which is legal). I actually learned C by reading the comments. Small piece of history - Cromix was written single handedly by Roy Harrington who left Cromemco to found Informix. Having said that - Mesa/XDE was awesome. I am sure Mesa/Cedar was even better.