It’s not really a chat, but there are comment plugins using third party servives that work really well:
- breakzplatform/tw5-github-comments: GitHub comments for TiddlyWiki5
- you could implement something similar to webmention with just some wikitext: New Features in TiddlyWiki 5.3.0: HTTP request and deserialize operator - Tips & Tricks - Talk TW. User wishing to leave a comment would be required to create a specific tiddler on their wiki, then your wiki could fetch these tiddlers, but it will only work if you already know the url of the commenter’s wiki. Or just use the webmention service directly, I’ve seen it on several front end dev websites.
- You could also do that with google sheet My new commenting system on Google sheets and Google foms. Test it please - Discussion - Talk TW (tiddlywiki.org), Can I use tiddlywiki to create intake forms and have the user submit them via email? - #4 by Theophile