http://gsd5.tiddlyspot.com/ is abandoned, but I’m using it anyway on a private Tiddlyhost site and it works pretty well for GTD.
Looking now I can see the underlying TW version is 5.1.9. I didn’t try upgrading it, so that might be a blocker depending on how well it runs in the latest version ofTW.
You need to follow the guide at Using a 5.1.23 or earlier version of TiddlyWiki · simonbaird/tiddlyhost Wiki · GitHub to make it work on Tiddlyhost.
I’ve also admired Projectify — Manage projects in TiddlyWiki. but never used it. I’m not sure if it’s based on GTD specifically, but it seems like you could use it that way. Unfortunately it’s also no longer maintained IIUC.