Not Wikilambda was an unofficial test wiki for the WikiLambda software. With the launch of Beta Wikifunctions, it became redundant and was retired on 30 October 2022 (T314880).
If you want to do something with the former contents of this wiki, a partial SQL dump is available, containing the most important MediaWiki database tables. (The full database contents are also available, but not publicly; if the dump is missing a table that should be public, let me know.)