When I ask around, I don't hear about it in use locally (edit: that's actually not entirely true, Blizzard uses it and maybe some of the other local game shops, but I don't see it anywhere else locally). I met someone at a conference a year or two back who was using Kong. That's been it. Maybe I'm just missing it but I don't really see widespread use.
Its such a simple but powerful language, has one of the best interop apis with C and I love how they approached coroutines.
It's really a shame it doesn't see wider use. We used it to ship all our game logic on the PSP, 400kb prealloc block and it worked like a charm.
Edit: And of course in Magic Lantern, for Canon EOS DSLRs https://magiclantern.fm/
Redis[2] lets you write internal scripts in Lua.
Edit: Forgot Torch[3] which is great for generating nonsense with RNNs.
I think it's definitely getting more of a foothold in the world outside of games.
[1] https://konghq.com [2] https://redis.io/commands/eval [3] http://torch.ch