Download of ShareLaTeX 0.1.3 for Mac was on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The application belongs to Productivity Tools. This free Mac application was originally designed by ShareLaTeX. 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.
From the developer:
ShareLaTeX is an open-source online real-time collaborative LaTeX editor. The app makes sure that you're always up to date with your collaborators and what they are doing. You can see where your colleagues are typing directly in the editor and their changes show up on your screen immediately.
You may want to check out more software for Mac, such as Combine PDF's or MakeDocJ, which might be similar to ShareLaTeX.