Just me again! :) I was about to make a post about this and found this one and I think it's related.

Think about a physical bullet journal and how people use trackers there. This could be implemented as something as simple as a table, like a small spreadsheet.

Allow the columns and rows to be labelled and customised, then the boxes could be any range of colours and a customisable key. I'm attaching a few photo examples of how they'd look on paper.

This could probably be integrated with habits somehow to get habits to display as a chart, and/or have an option for habits to be just check/uncheck OR set a colour when it's done and have a colour key.