restricter
Adds restrict mode checking to your program by rewriting operators into function-calls

asserter
C-style assertions with great error output
Assert(f(x) === 3)

logger
Formatted logging with great detail (file, function, line)
Log("Formatting via {0}", "Fmt") or just Log()

watcher
Trap (watch) object modifications for debugging purposes
Watch(o, "age", function() {
  if (o.age < 0) {
    throw new Error("age out of range");
  }
});

bitwiser
Requires annotation for bitwise operators | and & to avoid mistakenly using them instead of || and &&
var y = (/*@bitwise*/ x | 3);

stringconverter
Converts "" + expr and expr + "" into String(expr)

annotater
Internal plugin used by other plugins. Lets you match annotations and execute code with no effort Annotater(/\/\*+\s*@loose\s*\*+\//,
  function(node, match) {
    node.loose = true;
  }
);

annotation-printer
Dumps all your /* @annotations */

--tree
Dumps the syntax tree in an easy to read format, used when developing plugins

--source
Prints the shaped source code. This is often the final plugin/builtin used in a pipeline