Evernote is an outstanding application for capturing just about anything you want from wherever you want and finding it again! The Evernote search facility is awesome (here’s why), even when I don’t tag resources all that well, Evernote finds them again! I would recommend it for both teachers and students and have included it on the organisation page of the student version of this site.
Create a note using a phone or any web browser or use a desktop application. See this link for a short introductory video and a video library with many helpful tutorials. Evernote have also created a clear guide to getting started.
As a teacher I use Evernote all the time and have a notebook for each class I teach as well as numerous other notebooks. I also use Evernote shared notebooks as a way of sharing information, for example see Mathematics videos, QR codes and very appropriately some Evernote links! Having used a shared notebook to share some useful resources with students at school, some students then created their own accounts.
The free version of Evernote is excellent and more than adequate for millions of users!