Features:
Active pen (digitizer) support.
Very fast response to pen strokes.
“Fountain pen” mode supports pen pressure data, more pressure = thicker line (requires active pen)
Pinch-to-zoom.
Double-finger tap to zoom.
Two-finger move gesture.
Pen strokes are vector art, zoom does not pixelate your writing.
“Pen only” mode (optional) disables touch input while writing.
Android 3.x hardware accelerated graphics.
Open source (GPL), so your notes are not stuck in an opaque file format.
PDF export (save to SD card, Evernote, Share).
PNG (raster image) export.
Can backup/restore your data.
Ruled/Quad background paper
Tagging for pages so you can group them together.
Switch between multiple notebooks.
Undo/redo.