Another alternative, admittedly not open-source, is Recollectr (disclaimer: built by me.)
Recollectr was inspired by prior projects like Notational Velocity but aims to be a lot more - omnibox, markdown support, reminders; and for paid users: revisions, note-linking, and sync. I built it because I felt like other note-taking apps just weren't fast enough and they broke my concentration.
It's quite late here but I'd be happy to answer any questions tomorrow!
I was just checking out the site on my iPad. Only the top image loads and the rest are white boxes. I disabled all content blockers and reloaded but the problem persisted. It might still be a local problem, but now you have a heads-up that something MIGHT be wrong.