For marketing emails, Mailerlite has a generous and featureful free tier.

Zoho mail is damn good on the free tier.

Google forms / surveys.

GitHub of course!

Netlify is also a free CD / CI perhaps? You can run a script in a container on every deploy.

For seo, semrush has a good free tier for keyword research. There are other nice free tools like screamingfrog and keyword shitter.

Azure has some free forever tiers for functions and web apps but they are very basic.