Downloading Appcastr 0.1 for Mac from the developer's website was possible 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 application is included in Developer Tools.
From the developer:
Appcastr is a simple utility for Mac developers who publish updates using the Sparkle update system (or any other update system that uses Appcasting to publish updates). Appcastr provides a GUI interface for creating and editing appcast files that is slightly easier & quicker than just editing the raw XML file. Appcastr is currently in the early stages of development and is targeted towards making appcast files for the Sparkle update system.
You may want to check out more Mac applications, such as CVSServerSetup, Mopho LE or jKaiUI, which might be related to Appcastr.