Download of Oyster 1.4 for Mac was available from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. We recommend checking the downloaded files with any free antivirus. This Mac app is an intellectual property of RED When Excited Ltd. The program is categorized as Developer Tools.
From the developer:
Oyster helps you interactively build and test regular expressions--which aren't the easiest things to build and debug--storing each "pearl" in an easy-to-access library.
With powerful syntax highlighting, dynamic updates of matches, and the results of replacement patterns in test text, it has never been easier to build and test your regular expressions.
You may want to check out more Mac applications, such as Rock Guitar For Dummies or PithHelmet, which might be related to Oyster.