Top 2 file-monitoring open source projects

Watcher is a daemon that watches specified files/folders for changes and fires commands in response to those changes. It is similar to incron, however, configuration uses a simpler to read ini file instead of a plain text file. Unlike incron it can also recursively monitor directories. It's also written in Python, making it easier to hack.

Prometheus exporter gathering metrics about file size, modification time and other stats