On the Symfony blog they've officially announce their latest virtual Symfony Hack Day coming in March (on the 12th). This event is a concentrated effort from the project and developers to come together and solve issues over several hours.
Symfony has always been a project driven by a huge and active community. [...] Because Symfony has a predictable release schedule, we know that feature freeze for Symfony 3.1 will be at the end of this month (March). That makes the next few weeks of development really important!
That's why we've decided to organize an online hack day, and I would love if you'd join us. If you're an experienced contributor, great! If you're new, even better! This hack day will focus on teaching you how to contribute.
The event will be happening March 12th from 3pm to 8pm CET / 9am to 2pm EST and will focus around the #symfony-dev channel on the Freenode IRC network. They'll be focusing on how to get started contributing to the framework including a mini-workshop showing how to triage issues to creating a pull request.