What is this?

[joe at actionline.com]

What is this? ...

- - - http://www.upquick.com/temp/what.this.jpg - - -

I inadvertently hit some combination of keys and this popped
up on my desktop.  Don't know what keyboard sequence did this
(but I'd like to know) ... and I don't know what it is or
how to use it ... although it appears to be some kind of
desktop post-it-note.  Can the color and size be changed?

What is it, how does it work, and where can I find more info?