The Haxe programming language (https://haxe.org/). It's insane how unpopular this is compared to its value.
"Haxe can build cross-platform applications targeting JavaScript, C++, C#, Java, JVM, Python, Lua, PHP, Flash, and allows access to each platform's native capabilities. Haxe has its own VMs (HashLink and NekoVM) but can also run in interpreted mode."
It's mostly popular in game dev circles, and is used by: Nortgard, Dead Cells, Papers Please, ... .