Cobalt is a Lua implementation for Java, designed for use in the Minecraft mod CC: Tweaked. It is based on LuaJ 2.0, though has diverged significantly over the years.

Cobalt is a (mostly) compliant implementation of Lua 5.2, with several interesting additional features:

• Backwards compatibility with Lua 5.1 (getfenv/setfenv, goto as an identifier).
• Backports much of the Lua 5.3 and 5.4 standard library.
• Allows yielding anywhere within a Lua program, including debug hooks and inside any native function.
• Support for interrupting and resuming the VM at arbitrary points.
• Efficient concatenation of strings using ropes.

Don't.

No seriously, don't. Cobalt is developed in-sync with CC: Tweaked, and so grows and changes according to the mod's needs. There is no guarantee of API stability between versions. It makes many design decisions which make sense for CC, but not for anything which needs a normal Lua implementation.

Instead I recommend using one of the alternative Lua implementations, like LuaJ, JNLua or Rembulan.