Path of Exile, a free-to-play MMOARPG, has been in closed beta testing for quite a few months now, but developer Grinding Gear Games are going into open beta very soon. The public beta test is meant to stress the servers, which is often among the last steps during a beta. From the FAQ:
The Path of Exile Beta servers will be open to the public for the weekend of March 30-April 1. Below is a list of answers to frequently asked questions, explaining the details of how it works.
More information can be found on the FAQ page and the game’s website, including a nifty countdown timer for fans waiting in anticipation.