Platform: Android, Free
Files Go is Google's file management solution for Android users. It tracks your phone's available space while also being a junk sorter and file sharer on the side. The UI is identifiably Google and it comes with a lot of in-depth recommendation tabs for files you can delete or sort.
FX File Explorer
Platform: Android, Free/$2.99
FX File Explorer is a relatively new app but it's got a lot more going for it than the usual. Apart from the usual useful sorting and deleting features, it comes with a network storage feature and support for archived encrypted files. There's even a text editor and the best thing about it is that there are no ads nor does it track your device.
Platform: Android, Free/$3.99
If you've rooted your phone then this the explorer for you. While it's not the cleanest looking app, it is constantly updated bringing in new features with each update. You will get limitless root access, APK binary XML viewer, the ability to change a file's owner or group, MD5 support, and much more. While the features are limited on the free version and just called Explorer, if you want the full experience then paying for it is the way to unlimited access.