Oops! The XNOR schematic is now updated to make it not fail miserably. Also, I remembered to put the truth table in this time. Here it is.

One thing I forgot to mention about the XNOR gate in a balanced ternary system is that the truth table is also the single-trit multiplication table.

-1 * -1 = 1

0 * 0 = 0

1 * 1 = 1

-1 * 1 = -1

This isn't super-useful since a bunch of XNOR's in a line aren't going to give you a multi-trit multiplier circuit, but it could be useful as a tritwise operator. Assembly programmers and embedded programmers do all sorts of wild sorcery with bitwise operators in binary where they only have between 6 and 15 (depending on the programming language). Just think what people will come up with when they could have *thousands* of tritwise operators available to them...