What I'm looking for is something that builds C++ code every night or on every commit, and then, crucially, runs some commands to create a zip or a package which can then be added to a "Release" on GitHub.
I know there's travis-CI, which automatically compiles commits, and it can run for example a CMake INSTALL target and then CPack, which would create a zip or installer package. But it's not possible to upload these files to GitHub or display them somewhere.
I was thinking that maybe there was another service for that available which integrates with GitHub, but couldn't find any Google hits whatsoever. Preferably this would be separate from travis-CI, since on travis you would run debug-like builds (static analysers etc.). While for a release you want to deploy, you'd put release flags, build documentation, etc.
This is for an open source project so I'm looking for something that does this free for open source projects, preferably without setting up own server infrastructure.
There are a few related posts like Travis-CI Auto-Tag Build for GitHub Release or a travis section on deployment but they haven't really answered my question.