RegExr - RegExr.com is an online tool to learn, build, and test Regular Expressions.

eBooks.com - eBooks.com is a leading retailer of ebooks, with a vast range of ebooks from academic, popular and professional publishers.

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.

Kobo Books - Kobo Books is a best in the class eBooks and eReadering apps for many reasons.

rubular - A ruby based regular expression editor

Harlequin - Harlequin is a bookstore that sells paper books as well as eBooks. The store mainly deals in the genre of romance novels.