Teal – A statically-typed dialect of Lua

Is it implemented as a compiler, tl, which compiles .tl source code into .lua files? Who knows

Isn't that called a transpiler?

"Transpiler" is a common term for source-to-source compilers in the industry, but compiler is the more general term (i.e. a transpiler is a kind of compiler). In academia, the term "transpiler" is somewhat sneered at. A source-to-source compiler is still a compiler, because conceptually compiling into assembly is also technically source-to-source.