Simple sketches inside mainly text notes on tablet?

[AndyDent 76]

Is there a third-party app which lets you do simple diagram sketching inside a note?

 

I have been playing with something that lets you do box and arrow type diagrams very quickly, using a variant on the DOT syntax from Graphviz, but I keep also finding myself wanting to just do little napkin sketches. (I'm designing a house and there are odd ideas I scribble.)

 

I also want to accompany my sketches with my usual long-winded typed notes and don't find either PenUltimate or Skitch helping.

 

I have iPad, Android and Surface RT tablets so something for any of those would keep me happy.