Calibre Companion is a fully-featured mobile interface to calibre. Developed by a calibre contributor (MR's very own @chaley, who created templates and plugboards and custom columns among other things
), it costs $3 and allows you to connect wirelessly as a device. It allows you to sort by any metadata calibre has on tap.
It does not come with a builtin reader, rather it organizes/filters/searches your books and when you tap on a title to read it, CC will offer to open the book in whichever other ereader app(s) you have installed.
If you want to do fancy metadata sorting on your device, Calibre Companion is king.
