This application is still in beta and intended for usage with a stylus and a keyboard; it will mostly ignore touch input. (A bit more information can be found here.)
Space
Switch between drawing and selecting
Z
Undo
S / O
Save or Load SVG
C / X / V
Copy or cut selection, paste
⌫
Remove last element or selection
E
Extend (or with Ctrl: clip) SVG area vertically
P
Insert picture (PNG or JPG)
H
Approximate a horizontal/vertical line
K
Approximate a circular arc
R / L
Rotate clockwise/counterclockwise by 90 degrees
F
"Flatten" line (via downsampling)
1–9
Select drawing color or color for selection (1=black is default)
0
Select drawing color white (for fine-grained erasing)
J
JavaScript calculator (draggable by title)
B
Show auto-generated backups
+ / -
Change default stroke width
ESC / Q
Dismiss / quit (subject to browser approval)
F1
Toggle this help information (draggable by title)
R, L, H, K, and F act on the last stroke or the current selection and can be applied more than once. You can use PgUp, PgDn, Home, End, and the up and down arrows for vertical scrolling. The four arrow keys also move the selection around. When scaling a selection, the square handles preserve the aspect ratio, the circular ones don't.