How is this different from a job board or an agency?
Short answer
A job board assumes a salary and a hiring process. An agency assumes a retainer and a client relationship. Most of the arrangements we are interested in are neither — revenue shares, equity splits, straight swaps of skills between two people who found each other and decided to work together.
The longer version
This question comes up inside a longer piece on the same problem. If the short answer above raised more questions than it settled, the full article has the reasoning behind it.
What Push & Pitch Is, And Why It Might Not Exist