Tinyboard is a light-weight, fast, highly configurable and user-friendly imageboard software package released under a non-restrictive open-source license. It is written in PHP and has few dependencies.
Currently there is not. SQLite support was something I looked into, but it'd be near impossible to implement since Tinyboard uses numerous functions exclusive to MySQL/MariaDB.
If not, it would be a sick addition, specially flatfile so it requires less dependencies to run.