What are you most successful side-projects / passive income sources in 2015. Previous incarnations: 2014 https://news.ycombinator.com/item?id=8107588 https://

What are you most successful side-projects / passive income sources in 2015. Previous incarnations: 2014 https://news.ycombinator.com/item?id=8107588 https://news.ycombinator.com/item?id=8107588 2014 https://news.ycombinator.com/item?id=7094402 https://news.ycombinator.com/item?id=7094402 2013 https://news.ycombinator.com/item?id=6661536 https://news.ycombinator.com/item?id=6661536 2012 https://news.ycombinator.com/item?id=4639271 https://news.ycombinator.com/item?id=4639271 EDIT: added whitespace for para.