Huge collection of customisations and tweaks from Ton Gerner.
http://tongerner.tiddlyspot.com/
I am a longtime user of TiddlyWiki Classic and still use it daily since you can't do everything in TiddlyWiki 5 (yet) ;)
I started experimenting with TW5 at the end of September 2013 (alpha10). Since I missed a few things in the layout I got used to in TiddlyWiki Classic 1, I started with modifying the layout of TW5. To share my knowledge, I made a few guides about these 'modifications'. The guides started as a non-linear personal web notebook (yeah, the subtitle of TiddlyWiki!). I started experimenting with layout things and used TW5 to document my experiments.