GerbLook is an online viewer which renders images so you can "look" at "gerber" files. Gerber files are used for manufacturing printed circuit boards (PCBs).
Do you store uploaded gerber files?
Not unless you ask us to. Well, we do store them on disk temporarily while generating the images. Then unless you choose to save them, they are deleted from disk as soon as rendering is completed (or fails), within the same web request.
How are the images created?
Using Gerbv to render the gerber files to png images and then using some ImageMagick magic to merge and apply color to the images.
Why are the images a little bit jaggy?
Antialiasing is not turned which is what makes the nice soft edges you see on some images. This leads to slightly more accurate though not quite as pretty images.