* openlayers, but vector tiles have no web GL support there
* Procedural GL JS
* deck.gl (from Uber)
* harp.gl (from HERE Maps)
Leaflet is also great.
If you're doing any sort of front end GIS I recommend openlayers above all else including mapbox.
But I suspect 99% of users just need basic maps. Leaflet is great for that.
They removed this support in some previous version, I think.
Or do you have a link to a pull request or issue?
(IMO Leaflet is dead now that the creator is working since several years for Mapbox)
What someone can see as less development activity is simply a sign of a mature product that doesn't need many new features and changes to remain useful — focusing on the core basic mapping needs has always been its goal, and it continues to adhere to it.
What I see or meant as a sign of "dead" is that there will be no new features that Mapbox GL JS has but that are critical for future applications. Like proper or inbuilt vector tiles support.
Unfortunately that whole business unit got canned and the code is now gathering dust somewhere :/ would have loved to open source that one
I'd encourage you to reach out and ask for permission to release it. In the past I've found that the sticking point was usually copyright assignment rather than the release per-se (with a side helping of worry over hidden IP violations), so get them to release a tarball under a permissive license like MIT/BSD, even if your intention is to immediately fork it.
Basically, if you can manage to do the work for them so they can just rubber stamp the release, you can probably get it done.
I thought one of the primary features of Leaflet was its modularity. Would built-in vector tile support be an anti-pattern?
I've perpetually run into memory leaks and Max gpu issues whenever I try to use WebGL stuff in Openlayers depending on which browser I use.
Something will work fine in Chrome but max out my laptop's discrete card in Firefox until my laptop thermal throttles.
If you want a concrete example of this I would be happy to put together a reproducible example for you.
It does 3d, 2d, vector tiles, client side geoprocessing, and plenty of open data/service types
I'm keen on industrial archaeology and it's really helpful to have 3D visualisations of sites like old quarries.
Stand-alone 3D models can be done like  and the detail is substantially better compared to the map 3D views  (pits are pits again!) but I want to embed these into a website and start overlaying other data - just like I can with Mapbox maps.
2. https://felixpalmer.github.io/procedural-gl-js/, search for Llanberis
I have seen in demos coming from a few construction projects using this.