Request Tracker (aka rt) is a request tracking tool we use for various purposes. It is available as an open source product or a fully supported, paid product from https://bestpractical.com/request-tracker/.

RT is written in Perl, is very old, very stable, and very up to date. We like it because it is also readily extensible. Anyone conversant in Perl, who is also willing to go through the programming manual (such as it is) can customize RT very easily.

Note: the community version has good documentation, but there appear to be assumptions of knowledge in a lot of documents. Be prepared to do some searches.