Indie developer CoMiGo has put out a new Bitsy-like interactive fiction engine.
It has a few more advanced features that some people might find useful.
I haven’t checked it out yet (it seems to be hanging on my PC) but it looks promising.
I’ve used his other game engine, Ct.js, for other projects. It’s very straightforward and easy to learn.
Efficiency does seem to be an issue, at least for me. A development tool coded in HTML+JS and outputting HTML+JS is hard to run without lag on low end hardware. Maybe some people will have better luck. There’s still a lot to like.