Atheme is developed by atheme.org, an open-source development collective. Anyone can participate in the Atheme development process through GitHub. Contributors with an acceptable skillset and broad vision for the project are given commit access.
Atheme was originally built on top of Shrike, a legacy minimalistic services package. The developers of Atheme decided that Shrike was a good basis to build a more full-featured services package from, based on their previous experience of contributing to Shrike. Little of the original code from Shrike remains, however many design concepts do.
Atheme is extremely scalable, being used on IRC's current largest network, freenode. The scalability of Atheme, as well as other popular IRC services packages, was put to the test in the 2010 IRC Services Scalability Shootout.