Zerocoin implementation that is supposed to launch early this year:
http://moneta.cash/technology.html
https://github.com/MonetaOfficial/moneta

I think it is basically a rebranded version of Zerovert, which was a closed-source implementation released last year. One of the creators is one of Matthew Green's former students.

With that being said, it's still unproven technology, and I think there are some issues with launching the currency in a trustless manner, so for now Monero is probably most bestest.