There's also obsidian-export[1] that converts the few things that are not plain markdown (`[[links]` and `![[links]]`).
To be honest, obsidian not being open source doesn't bother me too much, what is important to me is that I own the data and that it is in a fairly common format so i can move it to another software in 10 years. An open source software with a weird binary format to save the data will probably do more harm in the long term