I'm surprised that they developed a brand new time tracking tool. From my limited experience, it seems Deltek Time & Expense is the most popular time tracking application in the government / associated contractor space.
Time-tracking keeps getting reinvented because no one's solved it definitively yet. I don't think anyone ever will, either; time tracking relies too much on individual context for it to be wholly standardized.
Like everything 18F produces, Tock is a work of the US Government and is in the public domain. There's a link to the GitHub repository in the blog post (https://github.com/18f/tock). We don't intend to launch Tock as a service, rather, it's something we made for internal use that is open for others if they find value in it.
https://www.gsaadvantage.gov/ref_text/GS35F0004P/0NIRVO.31QO...