Windows/Mac/Linux: VLC is one of our favourite video players out there. The release of version 2.1 packs in a lot of new features, including significant improvements to how it handles outputting videos to mobile devices like Android and iPhone.
The big improvements added in VLC 2.1 are underneath the hood. These include support for a lot of new audio and video codecs, 4K support, and a whole new set of options to efficiently send video to the iPhone and Android. You can find all the new improvements over on VLC's update log, or just download the update and start using it for free.
VLC 2.1 (free)