Diigo 
An all-purpose digital library, Diigo allows you to bookmark links, annotate webpages, save notes, upload pictures, organize items by types and tags, and share annotated pages with friends.
Your simple, but powerful notebook on the go.Add text note, take picture, import text message, add bookmarks to your library; organize text note, picture, bookmarks etc into lists; sync data with diigo.com; mark webpages as "read later" in desktop browsers, then read it on the phone. Widget on the home screen.
Organize your thoughts, course content, and notes visually on your iPhone, iPad or Android device with the following free mind-mapping programs.
SimpleMind+
SimpleMind+ is a free mind mapping tool that turns your iPad, iPhone, or iPod touch into a brainstorming, idea-collecting, and thought-structuring device.
SimpleMind Free for Android™ is a mind mapping tool that turns your android phone or tablet into a brainstorming, idea collection and thought structuring device. The Free version comes with basic but powerful Mind Mapping features.
Pearltrees
Pearltrees is a place to collect, organize, and share everything you like on the web. Collect web pages and turn them into pearls. Organize your pearls into pearltrees based on your interests and enrich your collection with pearltrees from other community members.
Tired of hauling around stacks of flashcards? Check out these free flashcard apps available for the iPhone, iPad or Android devices.
A+ FlashCards Pro
A+ FlashCards makes learning content easy. Features include: user-friendly interface with clean design, leitner spaced repitition, quizlet interoperability, in-app card creation (including text, audio, and images), and much more.
Flashcards [+]
Download millions of flashcards with this app or create your own. Additional functionality includes: quizlet interoperability, answer tracking, and the ability to hide learned cards.
StudyDroid Flashcards 2.0 Free 
Create flash cards online or on your phone, then sync them.
Make flashcards and study anytime, anywhere with STUDYBLUE digital flashcards
