ClipNinja 2.1 for Mac could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this app available.
Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. The software lies within Productivity Tools, more precisely Clipboard Tools. This Mac app is an intellectual property of Libor Huspenina.
From the developer:
ClipNinja is a lightweight clipboard history manager that enables you to effectively work with clipboard history, select, pin and paste recent clipboard items. ClipNinja focuses on productive clipboard item selection and pasting as fast as possible, without using the mouse. You can pin multiple clipboard items at the top so you can swiftly paste them when needed. Once you're done with some items you can easily delete them.
You may want to check out more Mac applications, such as Global Hotkey, iPasteboard or AutoClips, which might be similar to ClipNinja.