Why Download ZZT Worlds From Alternate Sources?
By acquiring ZZT worlds from other sources, you're helping to support the developers in ways that the Museum does not. Most files available on other sites are found on aggregate sites such as itch which provide anayltics letting authors see how often their world's page was viewed and files downloaded. Increasing these metrics isn't just an ego boost for the author, but may be used when determining where the file is displayed elsewhere on the site for users browsing content. Acquiring files from these sites can help spread a ZZT world to an audience not specifically looking for ZZT games and subsequently also help introduce ZZT to a wider audience.
Additionally, non-Museum sites also provide payment systems allowing authors to use "Pay What You Want" models or set an explicit price on a download. The Museum of ZZT will not freely distribute any files that require payment to download.
For better preservation, file viewer support, and in some cases the ability to play in the browser, these freely available files are are mirrored here and still available for download from the Museum of ZZT.
Please note that if you're trying to download a specific revision of a world, what is available on the Museum of ZZT and what is available on external sites may differ. Double check version information and filenames to make sure you're downloading what you're after!