What automatic build systems do you prefer to use in your projects?

I most often use Jenkins and GitLab CI/CD for automatic project builds. Jenkins is convenient due to its flexibility and a large number of plugins, which allows integrating builds with various tools and testing. GitLab CI/CD is well-suited if the project is hosted on GitLab — everything is built-in and easy to configure through .gitlab-ci.yml.

I also sometimes use Travis CI and CircleCI for open-source projects, as they provide free resources and simple configuration.

An example of a simple pipeline in GitLab CI:

stages:
  - build
  - test

build_job:
  stage: build
  script:
    - go build ./...

test_job:
  stage: test
  script:
    - go test ./...