First of all, the concept of a Mantis user funding the implementation of a feature, funding of a bug, or customisation of Mantis is already covered by our consulting practice. However, this is currently a manual process, and for sure an automated strategy that would allow even more than one Mantis user to fund one feature will definately be useful.

I have been thinking about this for a while, I think it would be very useful for Mantis and for open source products that use it. I know that this method is implemented in a couple of Open Source projects like PHPEdit and I think Horde. The question is:

When does the sponsor commit and pay the money?
a. When the sponsor indicates the interest to fund an issue, they pay the money to Mantis Group which then directs it to the person who makes the development. If the issue is not resolved within an acceptable timeframe, then the sponsor can get his money back from Mantis Group.
b. When enough sponsors commit funds to an issue to cover its development cost, then payments are collected from all these sponsors before development starts (what if a sponsor can not be contacted, or changed his mind at this stage).
c. Sponsors commit funds, then developer implements the feature, then money is collected from sponsors (again, what if a sponsor can't be reached).

Implemented in CVS and will be included in 0.19.0.