Which tool would you choose to create a CI/CD system from scratch?

I would choose GitLab CI/CD.

GitLab CI/CD is integrated directly into the repository, which simplifies managing pipelines and code. It offers a wide range of features, from building and testing to deployment and monitoring.

Advantages of GitLab CI/CD:

• All-in-one: Integration with source code management, issue tracking, wiki, etc.
• Ease of setup: YAML files .gitlab-ci.yml are intuitive and flexible.
• Flexibility: Support for various runners (Docker, Kubernetes, Shell, etc.).
• Extensibility: Ability to use custom Docker images and scripts.
• Free plan: Sufficient for small projects and testing.

Example of a basic .gitlab-ci.yml:

stages:
  - build
  - test
  - deploy

build_job:
  stage: build
  script:
    - echo "Building the application..."
    - # your build script

test_job:
  stage: test
  script:
    - echo "Running tests..."
    - # your testing script

deploy_job:
  stage: deploy
  environment: production
  script:
    - echo "Deploying to production..."
    - # your deployment script
  only:
    - main # Trigger on main branch

Alternatives to consider depending on the project's specifics and infrastructure:

Tool	Description
Jenkins	Flexible, extensible, but requires separate installation and configuration.
GitHub Actions	Good choice if the main repository is on GitHub.
CircleCI	Cloud solution with good integration with GitHub and Bitbucket.

But for creating a CI/CD system from scratch, considering ease of integration and rich functionality, GitLab CI/CD is the preferred choice.