BChecksFTW is a publicly curated list of all BCheck rules available over the internet.

BChecks are custom scan checks that you can create and import. Burp Scanner runs these checks in addition to its built-in scanning routine, helping you to target your scans and make your testing workflow as efficient as possible.

Each BCheck is defined as a plain text file with a .bcheck file extension. These files use a custom definition language to specify the behavior of the check.

More info here