Harlequin - Harlequin is a bookstore that sells paper books as well as eBooks. The store mainly deals in the genre of romance novels.
RegExr - RegExr.com is an online tool to learn, build, and test Regular Expressions.
Kobo Books - Kobo Books is a best in the class eBooks and eReadering apps for many reasons.
Amazon Kindle Store - The Amazon Kindle eBook store is the biggest and most widely used eBook store on the web.
Expresso - The award-winning Expresso editor is equally suitable as a teaching tool for the beginning user of regular expressions or as a full-featured development environment for the experienced programmer with an extensive knowledge of regular expressions.