CI/CD Platforms & Tools
Gitpod
Automated cloud dev environments. 
styleci.io
Public GitHub repositories only
CodeMagic
Codemagic is a fully hosted and managed CI/CD for mobile apps. You can build, test, and deploy with a GUI-based CI/CD tool. The free tier offers 500 free minutes/month and a Mac Mini instance with 2.3 GHz and 8 GB of RAM
DeployBot
REST API to trigger deployments from GitHub, GitLab, and Bitbucket
DatoCMS
Offers free tier for small projects. DatoCMS is a GraphQL-based CMS. On the lower tier, you have 100k/month calls
Terrateam
GitOps-first open-source Infrastructure as Code automation for Terraform, OpenTofu, Terragrunt, CDKTF, and Pulumi. 
appveyor.com
CD service for Windows, free for Open Source
bitrise.io
A CI/CD for mobile apps, native or hybrid. With 200 free builds/month 10 min build time and two team members. OSS projects get 45 min build time, +1 concurrency and unlimited team size
ElegantCMS
Headless CMS builder
LayerCI
CI for full stack projects. One full stack preview environment with 5GB memory & 3 CPUs
Mergify
workflow automation and merge queue for GitHub — Free for public GitHub repositories
buddy.works
A CI/CD with five free projects and one concurrent run (120 executions/month)