Every job I've worked in has had CI that is in some way unsatisfactory for me personally. But, I tend to work on projects with lots of configurations and tests that I want to run.
So, I made Limmat as a way to get want I want out of the CI as a developer (which is often a bit different from what is needed from the CI for project health, and always different from what the CI infrastructure is capable of delivering). It started as an exercise to get used to Rust, but it turned into a pretty valuable part of my workflow.
Basically it adds a new point on the spectrum of <things that run tests>. It's more lightweight and easier to configure than CI, but it supports a more rigrous workflow than stuff like Bacon that just optimises for fast feedback.