Although not open-source, this superior (imo) note taking app is currently undergoing an extensive discussion over going open-source; see here (https://forum.obsidian.md/t/open-sourcing-of-obsidian/1515/207). Please help make it FOSS.
Also, there are claims that one can see the full source code without much effort but I haven't verified this.
It is inherently safe out of the box if one doesn't opt to use the sync and publish services (paid) because all ones files are always stored locally, to which obsidian has no access - even if one uses the sync feature since the files are encrypted (machine encrypted before sending, I believe). This is contrast to Evernote who I left once I found out that all of Evernote employee's can easily access customer notes, and they have a lot to do with Gulag (google), and have a board of directors, and all the other scary stuff that points to future privacy concerns waiting to happen - if they haven't already. (I bet a 3 letter agency has forcibly used Evernote at some point).
What do you think?