I was just thinking about Opa the other day - it looked nice but I never used it. People were worried about debugging through the layers of abstraction. Is it still "alive"? You write in the past tense...
It is not really alive as of now. But there is still space for a full stack language and Opa is relevant today. MLstate, the startup behind Opa, shifted to secure communication platforms (built with Opa) and was acquired last year but without Opa itself.
Many things we did became hype later (implemented in OCaml, a functional language, JSX before React - I know Jordan played with Opa before building React) and we still have bits that are missing is today's stacks. The ideal next step would be to join a foundation so that development on the project could resume.
Tierless programming languages did not started nor ended with Opa. Eliom is very well alive and kicking (disclaimer: I'm finishing my PHD on the topic), as well as Hop, Split.js, Ur/Web, Links, Websharper, ...
I was always very disappointed by the fact that the inner workings of Opa were never described in any way. I can't even really cite it in my PHD thesis, because the documentation for the early (and more interesting, imho) versions has completely disappeared.
