Ask HN: Founders, what was the major sourcing channel for your first 100 users?

Reddit.

1. I made an app for the colorblind in 2015 and got my first 100 (and more) users from the r/colorblind subreddit.

2. I made a breathing app in 2017 and got my first users from r/breathing, r/breathwork, and r/meditation subreddits.

3. I recently made a productivity app for the mac and got my first users from r/macapps subreddit.

Reddit is incredibly powerful if you are building something niche and are already a part of the community. Also, the results are compounding because some of my posts get good SEO traffic so I still get a handful of users from Reddit every day.

I know I'm getting old when I have to stop and check for satire at the mention of "a breathing app". That sounds like an Onion headline, to me. Glad you had success!