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ClassicZoo is a fork of ZZT by Adrian “asie” Siekierka, started in late 2020 and initially released in March 2021. Its goal is to improve the ZZT experience while sticking close to the original engine's feel and keeping full compatibility.

If you'd like to learn more about ZZT, the Museum of ZZT is a good place to start.

Major features

  • EMS/XMS extended memory support - allows worlds of effectively any size within specification, and makes existing near-limit worlds run more reliably on real hardware.
  • Increasing the board limit from 20000 to 65500 bytes.
  • Major CPU and memory usage optimizations.
  • Major editor enhancements: syntax highlighting, OOP import/export, STK color and element support, multiple patterns, block and OOP copy/paste, bugfixes
  • Fixes for crash/hang engine bugs, while keeping compatibility.
  • Subdirectory support in the file browser.
  • NEC PC-9801 port.

The complete list of features is provided in the changelog, which is bundled with ClassicZoo.

Many of these bugfixes enhancements are also maintained to some extent in separate branches, to allow easier re-use by other ZZT forks.


PC port

NEC PC-98 port


The libre version of ClassicZoo differs in toolchain only - it's compiled using Free Pascal, rather than Turbo Pascal. However, as FPC's current (as of 3.2.0) 8086 compiler seems to generate slower and bigger code in general, it is primarily provided for users who seek to achieve free software purism. If you're a first-time or casual user, you most likely want the non-libre version at this time.

Current version

ClassicZoo 4.13

Released on the 27th of May, 2021.

Other downloads

Previous versions

ClassicZoo 4.12

Released on the 13th of April, 2021.

ClassicZoo 4.11

Released on the 11th of April, 2021.

ClassicZoo 4.10

Released on the 6th of April, 2021.

ClassicZoo 4.03

Released on the 28th of March, 2021.

ClassicZoo 4.02

Released on the 27th of March, 2021.

ClassicZoo 4.01

Released on the 23rd of March, 2021.

ClassicZoo 4.0

Released on the 6th of March, 2021.


  • Q: Which build and executable of ClassicZoo should I use?
  • A: As a rule, you should use the default build. The PC-9801 build is provided for users of such machines; the libre build is provided for projects which do not wish to utilize non-libre code included by Turbo Pascal's compiler. Regarding the executable, “ZZT.EXE” should be preferred for general use; “ZZTRUN.EXE” removes the editor and some “?” commands, with minor memory usage and CPU benefits - this may be useful on very constrained machines (think 512-640K of RAM and an 8088).
  • Q: Should I use DOSBox or Zeta with ClassicZoo?
  • A: Both are likely to work just fine; however, please keep in mind that behaviours which work correctly in DOSBox, but incorrectly in Zeta, are always Zeta bugs and should be reported appropriately.
  • Q: I'd like to make a ZZT 3.2-compatible game. How can I ensure ClassicZoo's bugfixes don't get in the way?
  • A: The “?DCOMPAT” command in the editor build serves exactly this purpose. If enabled, it will emit a warning when most bugs fixed by ClassicZoo are encountered - including behaviours which are unreliable in ZZT 3.2, but not always a crash or hang (like double #BIND).
  • Q: How good is ClassicZoo's compatibility relative to ZZT 3.2?
  • A: As a rule, all games released for ZZT 3.2 should work correctly in ClassicZoo, and the two should be freely interchangeable for this purpose. I am, however, aware of some behaviours which are not emulated:
    • Some worlds which rely on arbitrary code execution exploits (like PortalZ or Hack the Matrix) which depend specifically on ZZT 3.2 may not work correctly. This may be improved in the future, but - for some of these worlds - may prove impossible.
    • The fix for the “conveyor destroys player” bug also prevents all usages of the conveyor for stat swapping. To the best of my knowledge, no game uses this behaviour deliberately due to it only being documented very recently - if one is found or created, the bugfix may be adjusted as necessary.
release/classiczoo.1625990260.txt.gz · Last modified: 2021/07/11 09:57 by asie