Github Actions
Github Actions is the CI/CD system of Github. It allows you to run multiple kind of pipelines on your code. It's based on Yaml files that you can put in your repository. It's a pretty simple way to setup action like testing your code, building it, doing some checks, etc. It's a pretty good tool to start with CI/CD.
I use Github Actions in lots of my projects. It comes in addition to Tekton for some of my projects. In Monofolio i use Github Action to run tests, security checks, code coverage, etc.