Waht makes the SQLite code base so special?

One thing I like about it is that it uses the fossil scm.

Fossil scm tracks files, not content (as git does). This property makes fossil an ideal scm for doing some kinds of static code analysis which need to track files across a history of renames. Try that with git.

I guess their approach to testing is one of the qualities that makes it stand out https://www.sqlite.org/testing.html