Tabber 1.1 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. The software lies within Productivity Tools, more precisely Office Tools. We recommend checking the downloaded files with any free antivirus.
From the developer:
Switch windows and apps with a Hotkey and improve your experience and workflow.
Activate wanted windows and apps with Tabber Window Switcher which is a Command+Tab alternative to switch windows.
See contents of windows Real-Time when switching windows. Switch Apps and Windows with a shortcut or set a custom shortcut to switch windows or to switch apps.
You may want to check out more software for Mac, such as TabbarTool or International Snooker 2012, which might be related to Tabber.