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

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.