I'm the author of mnm, an open source project to replace email & SMTP. (For the story, see mnmnotmail.org & twitter).
It's a self-hostable server and downloadable client, so it never occurred to me to do anything but open source. But I guess that's not the case for most indie SaaS apps.
Who all is building open source, and why? Why not?
I made an open source tool a while back. It was a vim-plugin, and I just wanted to make something cool for the vim community.
You can check it here: https://jerseyfonseca.com/projects/bujo
It's awesome to have people use my stuff for free, but I've stopped building open source tools for now because I want to try and generate revenue from the long hours I put in after work!