Basic chalkboard, white on black. Very easy to use, all lines same width.
Drawbacks: The only way to erase is to shake the device, which is easy with a phone but hard with an ipad. The blank slate is not black, but slightly mottled, like a real chalkboard after being erased. After shaking to erase, some of the marks remain, faintly, but seem to accumulate so the slate becomes greyer and greyer, reducing contrast.