We're starting a new series, periodically highlighting new tools and advancements that help to build immersive experiences on the open web. Look for more of these posts in the tools category. These can be new products, significant updates, or simply new discoveries.
A-Watch
A small library for building watch-like user interfaces in a-frame, supporting hand tracking. There is even a demo, and here is the announcement tweet with a brief video.

We'll get the scene in the Babylon.js inspector. The cool thing is that the XSML file is very easy to understand, for anyone who knows HTML.
As a personal aside, my one point of criticism is how much of the documentation, and even how much of the code, is written in Chinese. I strongly believe that computers should be used in English, and that having a lingua franca for technical work is extremely important, but I suspect this is now considered part of my 90s techno-optimism. Coming from a native English speaker it would also probably sound like some sort of xenophobia, luckily that's not the case.
Simulate 3D plants in the browser
Extremely interesting plant simulations by undergrad (serious kudos!) Max Richter. The graph editor is so nice to play with!