Prompted by an article on Z80 REPLs, readers share nostalgic memories of the built-in assemblers and monitor programs found in classic 8-bit computers like the Apple II, Commodore 64, and BBC Micro. Many commenters recall how these early, integrated environments were crucial tools for learning to program and reverse engineering software. The conversation also touches on the technical implementation of these features, such as the non-maskable interrupts used by freezer cartridges to invoke monitor routines.