While the language & feature-set might be a direct competitor to Lua, the license may make it a non-starter for many.
Lua: MIT: can be used in closed source software.
Jx9: Symisc Public License (basically the Sleepycat license): Very similar to the GPL in that all source code using it must also be open source upon distribution. Otherwise, a license must be acquired at some unknown price to use it in commercial software.
I think the Jx9 license is correct and acceptable for open source softwares since many open source projects embed BerkeleyDB which use this kind of license.
Lua: MIT: can be used in closed source software.
Jx9: Symisc Public License (basically the Sleepycat license): Very similar to the GPL in that all source code using it must also be open source upon distribution. Otherwise, a license must be acquired at some unknown price to use it in commercial software.