zxsp is a simulator for the historic Sinclair ZX home computer families. Main supported platform is Mac OS X. Versions for classic MacOS and old versions of Mac OS X are still available from the zxsp download page.
zxsp supports “.sna” and “.z80″ snapshot files, “.tap”, “.tzx”, “.pzx”, “.80″, “.81″, “.o”, “.p” tape files, excellent sound, precise screen and border effects, joysticks, mouse, a virtual tape recorder and virtual keyboards.
zxsp can load from and save to a built-in virtual tape recorder or a real-world cassette recorder or a real-world Specci. It also can dup real-world cassette tapes to “.tap” files or vice versa.
zxsp supports the black&white models ZX80 and ZX81 and the Jupiter Ace, the ZX Spectrum models with 16K and 48K ram, the +128, +2 and the +2A/+2B; including the Spanish and French versions. If you still own one of the emulated machines and find that the simulation does not match the original, you are welcome to contact me for further improvement. Just keep the original thing ready for tests. 
zxsp comes with a debugger with register edit for the main chips, a video beam position indicator, single stepper and memory disassembly. The machine can be throttled down to 1 Hz or overdrived to 20 MHz cpu clock. You can directly load Z80 assembler sources into zxsp.
What’s new:
Version 0.7.3pr4:
• Working on generic emulation of the b&w machines:
• Jupiter Ace: memory (3K), keyboard and video decoding. tape i/o mostly usable.
• ZX81: memory (1K), keyboard and highres SLOW/FAST video decoding. tape i/o mostly unusable.
• ZX80: memory (1K), keyboard and highres video decoding. tape i/o works.
• ZX80: tape loading fixed, automatic ram size for .o file if loaded with “Open…”
• Frequent crash when switching between models fixed
• Currently heavy internal rework, use the public version 0.7.2 if things do not work for you!
