Downloading TweetRails 1.0.0 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. We recommend checking the downloaded files with any free antivirus. TweetRails for Mac lies within Communication Tools, more precisely Social & Blogging. This free Mac application was originally produced by Takuto Nakamura.
From the developer:
TweetRails is a client app which allows you to view Twitter as a news ticker on your Mac. Tweet links and user icons can be clicked to open the landing page if you hold down the modifier key you set. You can also click on the hashtag to stream the search results. You can select the modifier key from the command, option, shift, and control keys. You can switch accounts and search keywords at Preference.
You may want to check out more software for Mac, such as ituwitter, Photo Download or TwitterTool, which might be similar to TweetRails.