Evernote seems to be an excellent site for students who wish to organize their learning! Using Evernote for free, you can save and categorize any piece of online information (including texts, videos and photos) that seems useful or interesting. You can even connect your Evernote account with your Twitter account by following @myEN on Twitter. In this way, you will be able to collect all your favourite tweets and classify them into as many Evernote notebooks as you want. You can learn more about its various features here.