Is it unlawful to enter a URL other than your own into the Scrawlr URL field?
Can the use of Scrawlr on a site the user doesn't own be construed as an attempted attack on that website? Or is the software, in and of itself, harmless?
According to some interpretations of U.S. law, yes, Scrawlr and just the simple activity of crawling someone else's site can be construed as a felony. The common security professional's understanding is that if you do not have written authorization, then your target can take action against you.
I am not a lawyer, so you should review your own legal counsel where applicable.