To add to what Jose has already said, if you really want to know exactly what has changed between two nightly builds, you can take a look at the version information in the about dialog (Help→About). For nightly builds, this dialog also lists the “identifier” (a long string of letters and digits) of the commit from which the build was created. You can then look up the commit identifiers of both builds in the commit list which Jose linked at the top of his post. Every commit after the one from the older build, up to and including the commit shown in the newer build is something that changed between those two versions. The descriptions of those changes can be a bit technical, and a lot of it is probably not very interesting from a user perspective, but it’s the best we have right now.