Recently Google announced a new program named "Google Season of Docs" (GSoD) which is aimed towards ensuring better documentation of open source projects.
Anti Grain Geometry (AGG) is a powerful raster graphics library created by Late Maxim Shemanarev, which is used as the primary backend in Matplotlib. However, AGG has a steep learning curve because of lack of documentation and active community development since 2006 (which can further be attributed to lack of documentation).
Proper documentation of AGG will not only lead to new tools built upon it but can also revive and reinvigorate its development.
Since AGG is an integral part of Matplotlib, I believe that the Matplotlib devs will be able to do this project the justice it deserves and guide the GSoD technical writers properly.