Bored of playing MineCraft alone? Want to join and play MineCraft on SMP? Want to play on servers without paying? I have the solution for you! Introducing MineShafter Squared.
MineShafter Squared is an open sourced proxy that tricks MineCraft in to thinking you own a premium account. But, you can only join MineCraft servers that use MineShafter Squared authentication.
1. First of all go to mineshaftersquared.com (will hyperlink once I'm allowed to.)
2. Follow the instructions on the main page and voila you are now able to play MineCraft on SMP.
All credits go to the great coder and maintainer of MineShafter Squared, I am just bringing this to your knowledge.