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* Typed Lua: https://github.com/andremm/typedlua (not actively maintained)

* tl: https://github.com/teal-language/tl a compiler for Teal a typed dialect of lua. (actively maintained)

There is also Luau and Ravi but I don't think any of them is official which was the original question

Indeed, Teal looks like it has the right brains behind it (author was involved with several earlier attempts at typed Lua) and is actively maintained. I'm personally watching it for future game development usage.

I believe he was talking about Pallene, which is being currently developed in LabLua

Paper: http://www.inf.puc-rio.br/~roberto/docs/pallene-sblp.pdf

Git Repo: https://github.com/pallene-lang/pallene

Shameless self promotion: https://github.com/Benjamin-Dobell/IntelliJ-Luanalysis