The DevWheels Licence is a standard licence that creators can assign to a copyrightable work. The licence allows copies of the work to be freely distributed, and allows derivative works to be freely distributed under the same or a compatible licence. Works under a DevWheels Licence can be used without charge for the purposes of evaluation, testing, and development.
The licence however differs from a totally free licence by allowing creators to require that certain classes of users pay before using their work in another way, and by requiring creators to forward to the creators of any DevWheels-licensed works from which they have directly drawn whatever these creators charge this same user to use this source work.
In this way, the charge for a work is distributed back through the derivation graphs of both the work itself and any separate but prerequisite works, compensating all contributors according to the value they've added, while at the same time allowing totally-open development.
Creation of the DevWheels Licence was motivated both by the advantages of Free and Open Source Software, and the difficulty of earning income from writing it in a way that doesn't compromise either openness or ethics.