If you're looking for a platform with a generous free tier for SMS, emails, and call minutes good for small projects or hobbyists, Contiguity is a good choice. This general-purpose communications foundation has a free tier with limited usage, so it's good for individual developers and small startups. It also offers pay-as-you-go and unlimited tiers for bigger operations, with pricing starting at $0.005 per SMS message and $0.002 per email.
Another contender is FlowCharts.ai, which has an economy class (free, limited features) tier. This platform is good for building and deploying smart forms, surveys, decision trees and workflows across many channels, including SMS and email. The free tier is a good starting point for small projects or hobbyists who need basic communication and feedback tools.
If you're interested in no-code backend development, Contember offers a free Developer Sandbox. The platform lets developers rapidly stand up custom software projects with AI and open-source frameworks. It's designed to be economical and good for small and medium-sized businesses, with a variety of modules for different business operations.