I was not aware of trkl. Well done! I wrote rmemo (Reactive Memo) which solves the same problems & is a similar size. Different semantics though.

https://github.com/ctx-core/rmemo

Nanostores is also small https://github.com/nanostores/nanostores.

And if you only need reactivity in the browser (not server side), VanJS is small & includes reactive primitives. https://vanjs.org/