Like Nexus already said, the most valuable asset to an open source project is its community and user base. Knowing who uses SFML and how they use it helps the library evolve in the right directions. Without feedback, all we can do is make assumptions based on what we perceive and that might not always be accurate.
That being said, we are always looking for people to test new feature implementations and report bugs. The more data we can collect, the more confidence we have in the test results. The last thing we want is progress on an issue to be blocked because of something unrelated on the reporter's system. Getting prompt feedback in regards to development is also nice to have. We've adopted a faster release cycle, which means we are more willing to commit less stable code to master hoping it will get tested by more users that way. The more people use master, and the more people report issues they have with it the faster we can respond and make sure everything gets fixed before the next stable release.
I don't know what policy your company has in regards to the version of SFML that it uses in its products, but if it is possible to test them against a master build of SFML and report whether the issues which have been declared as fixed are really fixed, that would be great. It would add to the confidence of newer code and accelerate the rate at which code can be considered stable. The reverse is true as well, if code is changed that ends up breaking your product(s), it would be nice to get a prompt report as well. The others and I are keen on slowly clearing out the tracker of issues and one way of doing that is by making sure newly reported issues are given higher priority so they can be dealt with while the reporter is still around and can provide information on how to reproduce the issue.
A few other random points off the top of my head:
- Free publicity is always nice . As stated in the licence: If you use this software in a product, an acknowledgement in the product documentation would be appreciated but is not required.
- Maybe this belongs to the first point, but testimonials are also advantageous. Every now and then, people come to the forum asking whether SFML has been used in commercial projects. There are a few projects that are known to us, and there are probably a few/many more that aren't, but without actual first hand proof, we don't have much to back up our claims.
- SFML is always accepting donations and we are working on setting up a somewhat usable CI infrastructure. There were/are discussions on whether we should get a dedicated OS X node, and I'm probably not the right person to ask about that . All I know is that it isn't something that SFML can afford right now considering the team works on it pro bono.