FYI, if anybody has questions, there are several YC alums who have joined the government in some capacity (healthcare.gov, USDS, Nava, PIFs), and are on HN.
What is the easiest and smallest way to get started/to help, without getting a job with the gov (which may not be possible for many folks) or without bidding for contracts? In other words, how to help from outside the gov? Is there a list of tasks somewhere that someone maintains that can be done independently?
A colleague at 18F built https://www.govcode.org/. It's a handy directory of U.S. federal government open source projects.
Best way would be to join the USDS "reserves"--they sometimes ask people to come for 2-3 weeks to do an evaluation of a government project. If you can get time off from your job, or you're switching jobs, I think that's a high impact way to contribute without necessarily joining fulltime.