This API makes it super easy to send calendar invite requests. Use it to create "add to calendar" buttons for your site, trigger calendar invites based on certain user actions, or automate team scheduling.

50 requests per month for free, then from ~$12 p/m

An API for scheduling social media posts. There are many social media scheduling tools, but finding a decent API to automate posting & scheduling is harder than it initially seems. The Buffer API, which I use, is no longer open for new customers. Ayrshare is an API first option that lets you schedule posts to Facebook, LinkedIn, Twitter, Reddit, and Telegram.

Free for 300 scheduled posts p/m, then custom