If you want opensource and local storage look up Dendron. It is a VSCode extension in a similar vein, uses markdown so easily track changes in git/etc as well.

Links to code:

https://github.com/dendronhq/dendron

Or Joplin (has extensions for Graphs as well).

Or Foam.

Link to code:

https://github.com/foambubble/foam

Unfortunately Obsidian is not FOSS. It does have an open hackable plugins API though. There are lots of open source community plugins.

Link: https://github.com/obsidianmd/obsidian-releases