I'm looking for a player (ideally Mac OS X or Android or online) which instead of playlist (you can play only one at time) has a concept of tags to organise songs.
So I can tag songs with as many tags as I want and then I can ask my player to play e.g. "childchood", "rock", "polish" tagged songs. It should be easy (1click) to add/remove tag from song and easy to filter songs by tags (e.g. simple text field).
I could find anything like this and even start thinking about writing one by myself. I cannot believe there is no such piece of software.