UICatalog 2.10 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.
According to the results of the Google Safe Browsing check, the developer's site is safe. Despite this, we recommend checking the downloaded files with any free antivirus software. The actual developer of this free software for Mac is Apple Inc. The program lies within Lifestyle Tools, more precisely Bookkeeping & Cataloging.
From the developer:
This sample is a catalog exhibiting many views and controls in the UIKit framework, along with their various properties and styles. If you need code to create specific UI controls or views, refer to this sample and it should give you a good head start in building your user interface. In most cases you can simply copy and paste the code snippets you need
You may want to check out more software for Mac, such as GHC Interactive System with Extensions, iMon or Book Magic, which might be related to UICatalog.