Easy to implement proof of shuffle
Andrew Neff's verifiable shuffle scheme A Verifiable Secret Shuffle and its Application to E-Voting is implemented by the DeDiS Advanced Crypto Library for Go

A working example program that uses the code is the server from the Riffle anonymous communication system.

Here's a "mostly finished" standalone implementation in Go, including a paper explaining the protocol: https://github.com/cjpatton/shuffle.git