Yes, IUP would have been the killer toolkit if it only supported OSX. I love the IUP API in both C and Lua.

I wish it had good OS X support too.

The best hope so far is probably what's described in this email: http://lua-users.org/lists/lua-l/2016-03/msg00019.html

Would have been better if they added OSX support to IUP and not re implement an entire toolkit.