It's the server/client for https://lichess.org/ which is a powerful online chess server. Scalla with Akka actors is used to provide realtime multiplayer chess (bullet chess games, where each player only has a minute or two to play an entire game, are very popular there). The client-side is written in TypeScript, and rather than use React for the vdom, they're using a vdom called snabbdom. https://github.com/snabbdom/snabbdom
However, I don't think the technologies he/she mentioned are little known. Scala, Akka and TypeScript are certainly well known. The last I heard, Vue was based on a fork of Snabbdom.
BTW, it may be worth notice that the code base of Lichess.org also uses Mithril. I used Vue in the past but converted my choice to Mithril afterwards. To me, Mithril is simpler to learn or use. My code using it is cleaner and easier to maintain. But this is certainly anecdotal and YMMV.
Scala, Akka, TypeScript, React...uh, where have you been?
Lichess is an impressive project, their chess app is not only excellent compared to everything else out there, it's incredibly efficient, and handles a ton of traffic with ease. I don't think the creators chose the stack without reason.
This is probably not the go-to stack but not for the reasons you've stated.