Yes, but on first glance (without a lot of digging) at the links here, only Pastery seems to be open source (ix.io says it will be...someday), and Pastery (as nice as it is--thanks for that link) is for a different purpose (exchange of code snippets).

Rwtxt looks like a nice, simple, markdown-based, easily self-hostable, open-source, personal notes wiki. Nice work! If there are others that more or less match this description (self-hosted, open-source, private notes repository), I'd be interested.