The Evo Factory creates and operates commercial web sites using b2evolution. They play an active role in the development of b2evolution.
They feel that fine tuning the power of b2evolution to their needs gives them a competitive advantage, and, putting their money where their mouth is, they make sure b2evolution is sufficiently funded to develop at a rapid pace.
This model is very similar to how Firefox is funded for example. Maybe on a smaller scale, though ;)
Note: in the past, b2evolution was funded by donations.