I started out with GitLab for their free CI and multiple private repos before both was available on GitHub.
I'm mostly using GitHub to share code examples as people are just more familiar with it. With GitHubs current offering I might completely switch in the not too distant future.
* GitLab for private repositories and CI (free)
* GitHub for public repositories (free)
* AWS for serverless backend & frontend hosting (free so far)
* Notion for milestones, sprint planning and notes (free)
* MailChimp for email campaigns and CRM (free)
* Webflow for landing page & blog
* Docusaurus for documentation, in progress
* Plausible for analytics
* Office 365 for email and documents
* Stripe for payments