GROU.PS serves you from a cluster of Apache application servers, proxied by a bunch of nginx load-balancers. All our operating systems are Linux based, more specifically a mix of Debian and Red Hat Enterprise Linux. Our database is open source MySQL, scaled thanks to a technique called database sharding. We run a set of Postfix for the outgoing email, and Apache James for incoming ones.

Our application is written in PHP. Most of our cronjobs are either shell or Python scripts. We use Java to handle incoming email.

As for storage, we rely on Amazon S3.