Examples of AMP-like JavaScript approaches?

Does anyone know of sites that have copied the AMP approach to JS/perf but not using AMP itself? It seems like the approach is interesting (custom elements with a core managing things). Too, there are good reasons why AMP itself may not be a good choice (e.g. if you need components it doesn't provide). But I'm struggling to find examples. Mostly the talk is just React or other similar libraries, which feel inappropriate for sites with mostly simple behaviour.