This project hasn't been updated for almost a year, is not fast, and the issues suggest that it's dead. Why post it?

I agree.

What's the recently updated, fast, actively developed alternative in this space?

This library has been "not ready for prime time" for at least 2 years now... :-/

These are all really nice looking, but the android radio buttons seem very user-unfriendly. I'm usually pretty good at sorting out indecipherable buttons and whatnot but they've got me stumped.

I guess some of these would be fancy on mobile, but the latency between action and the ultimate feedback is remarkably high. (as with any animation)

This would not work well in a product that end users use day in and out, often with keyboard savvy shortcuts to save time.

Macbook 2014, Chrome and it's super slow.

They aren't slow on my macbook/chrome (which is a bit older than that). Are you speaking of the actual timing of the animation, or the framerate? If it is the timing, that can be adjusted. For instance, in the css you'll find things like:

transition: -webkit-transform 500ms;

transition: transform 500ms;

Just change that 500ms to 200ms and it will take less time. The effects will be more subtle (so maybe not as good for "showing off" as in the demo), but probably a better experience.

Macbook 2012, Safari an it's super slow too ;-(

Most of them are not really smooth (Chrome 49 on Macbook)

It appears the project is all but dead: https://github.com/h5bp/Effeckt.css/graphs/code-frequency

I didn't get performant from this demo, but I did come across another lib that I starred on github https://github.com/daneden/animate.css it may do some of the same things and seems to be pretty active

Looks nice, but most of these show significant frame drops on my phone (Galaxy S6).

"Performant" :P

Not exactly sure what you mean, but the funny thing is that there seems to be no single-word translation from the German "performant" ("with high performance") to English. Or is it?

He means animations on that page are slow as hell.