Mac: Apple introduced tabs to Finder back with Mavericks, but if that's not enough for you, Commander One adds dual pane browsing, alongside a few other tweaks and options.
Commander One works almost like a plugin for Finder. Once it's installed, you get dual pane browsing, unlimited tabs, a variety of sorting options, an easy toggle for revealing hidden files, and more. It also adds a handful of new keyboard shortcuts to make moving files around a little less painful. If you're not a fan of how Finder does things, Commander One's a more than capable alternative. There's also a Pro version that adds in FTP support, Dropbox integration, iOS device mounting, a Terminal emulator, and more.