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Hi, there are a lot of uses to raspberry pi, one my favorites is to used it as cloud storage so you can upload and even stream music or video from your place to your phone, share files etc.
http://www.tonido.com/support/display/docs/Raspberry+Pi
In this guide there's a step by step how to install tonido on your raspberry and mobile and basic configuration,
I am here to help in case is needed,
Great week!