PaperPort Notes (free)

Function:

Note Taking: Users can take notes as typed text or free hand annotations.

Annotating Text: PDF files can be annotated. 

Audio Recording: Users can record the speaker during a lecture or make their own audio recordings. 

Works on:

Comments:

This a very versatile app. Supports highlighting, post-it notes, freehand drawing, and audio notes. The latest version supports Optical Character Recognition (OCR).  OCR allows you to take a picture of a printed page and it turns the words into editable text. Doesn't project well, so not a good tool for teacher modeling of annotation think-alouds. 

Resources:

Edshelf Overview and Review

Tutorial