The original Classic version of TiddlyWiki is still available at:

https://classic.tiddlywiki.com.

Note that the current version of TiddlyWiki is not fully backwards compatible with TiddlyWikiClassic. Content can be imported but will need massaging to adapt to the new WikiText format. A tw2parser plugin is under development that will allow faithful display of most content created for TiddlyWikiClassic:

https://tiddlywiki.com/plugins/tiddlywiki/tw2parser/