Musi for iPhone is a streaming music app that lets you build a music library that costs you literally nothing, with the help of YouTube. When you search through Musi, it's basically like searching YouTube for music. The only difference is that Musi only streams the audio portion.
You can start by searching for your favorite artists and adding the tracks you like. They are then added to your main library. From there you can sort songs into playlists however you'd like. Playlists are unlimited so you can create and manage them however you want. For many people, this may be a way to create albums. This is the only downside of Musi. Since it's simply searching YouTube for tracks, you need to add tracks one by one. It's not a huge deal if you don't mind creating playlists for artists or aren't the type of person that downloads entire albums anyways.
Musi also has support for AirPlay so you can stream anything you want to any AirPlay enabled device. Along with that you get background streaming as well so you can close out the app and continue doing something else while Musi continues to serve up tracks in the background.
Obviously Musi isn't an all-in-one music solution since it won't work if you don't have an internet connection, but it's a super convenient ones for folks like me who are finicky with music. I have a nasty habit of only listening to things for a few weeks and then never really returning to them again. For stuff like that, Musi is perfect since I'm not spending money on songs and tracks I won't even want to listen to in a few weeks.
If you give Musi a try, let us know what you think of it in the comments! Could you see yourself using it for music discovery and then only purchasing the albums and tracks you want to keep forever?