Neat tool for teachers. Need a quickly designed number line or graph paper. From NCTM and Illuminations, easy to create different options, easy to download as a jpg and then cut and paste if you want to use in another file.
Good for basic graphics needs that you might not be able to create on your own like nets and spinners.
Always looking for resources that help math teachers think about how to promote learning in the classroom. This synopsis of formative assessment research starts with Wiliam and Black, "Inside the Black Box" from 1998 and progresses forward from there. Some nice specific tasks that are supported by links to examples.