Apple announced High Sierra, the latest version of macOS, back in June at its WWDC. For many months now, beta testers have been able to test the software. It seems that the software is now ready for public launch. Apple has said that it will ship out High Sierra on September 25th.
Of course, High Sierra is completely free. It will run on any Mac since 2009. Keep in mind that this software update will break compatibility on older apps, include Apple's own Final Cut and Logic programs.
High Sierra introduces a huge lot of new features for users, such as a whole new Apple's own APFS file-system that will free up some more space on your Mac. In addition, the software will speed up certain tasks, backups should become easier, external GPU and VR support, and much more.