If you don't know what OPIE is, you can likely just stop reading this post now.
Apache Orthrus is a C library and user interfaces for RFC 2289, "A One-Time Password System (OTP)", also known as OPIE or S/Key.
If you have ever tried to compile OPIE on OSX, you might understand why I started this, its just painful and full of silly things.
Most of the Apache Software Foundation's FreeBSD machines use OPIE for our sudo accounts, and I've been using SkeyCalc, which was last released as a PPC Binary for 10.1 in 2002. Right now Apache Orthrus can do the client side of OTP, but I want to finish the project to include a PAM module and full verification support.
Patches welcome though, if anyone else uses OTP out there......