An unrestricted grammar for L = {w in {a,b,c}*: w has the same number of a's, b's, and c's}

First create an equal number of  A's, B's, and C's without regard to order. 
Then let them rearrange themselves arbitrarilly.
Then let each A, B, and C turn into the corresponding terminal.


S --> A B C S | e   // Create an equal number of A, B, C

A B --> B A   // Let them rearrange themsleves any old way
A C --> C A   
B A --> A B
B C --> C B
C A --> A C
C B --> B C

A --> a       // Replace each variable by the corresponding terminal 
B --> b
C --> c