One thing about Obsidian: it’s not open source. Even though it’s free to use—unless you start making money from that use, or want to use the upcoming sync and publish features—it’s somewhat closed, by which I mean you can’t see the code that comprises Obsidian. Having said that, the people behind Obsidian are very open about never wanting to produce software that will force you to keep using them; you will always be able to take your open files and go somewhere else if you want to.
Source: Obsidian: my new knowledge base or base for knowledge – Niklas’ blog