From Computer History Wiki
PC/370 is a simple System/370 emulator that simulates a few mainframe environments, and provides the means to build assembly programs on the PC, and run them.
PC/370 is generally considered obsolete, and is no longer needs to be paid for.
Links of interest
- http://www.billqualls.com/assembler/ A PDF copy of the book "Mainframe Assembler Programming" released by it's author.