I have seen many questions like https://elementaryos.stackexchange.com/questions/3361/anyone-successfully-activated-overgrive and GIMP crashes on launch or both not about elementary and about software . Are these questions on-topic on this site?
It is important to remember that most users are not heavily technical and will expect to just get an answer when they come here, rather than being sent somewhere else. To them, they are on elementary OS, and this site is where they get help for it.
And that is okay.
My suggestion is as follows:
- If it is a simple question regarding installing/running the program on the target OS, (though not a question regarding running the program on another OS), we let it slip. Some examples:
- How do I install application X?
- Where are the configuration files for application X located on elementary OS?
- X-app won't start. Aliens, or Gremlins?
- If it is a generic, OS distro-agnostic question about using the application, but not truly off-topic - we let the community decide. If after a time, the question is abandoned (and not answered or followed up), we close it. Example:
- How do I do X in LibreOffice Writer?
- How do I install openclipart on Inkscape?
- How do I add rules to UFW?
- If it is a highly technical question about a third-party app, and the community is not likely to be able to step up to answer it, then we should let the community vote to close as off-topic (they likely will).
- How do I make minecraft run as a Microsoft Flight server?
- How do I prevent my dog from eating my homework (whole) using Anti-dog-configurator-for-Linux-pro?
- These last two examples are deliberately ridiculous - to drive home the point.
Overall, remember, like I said at the beginning of my answer, users aren't typically heavily technical. They need our help, not a help desk or PBX system :)