Textbelt uses email-to-SMS to send texts for free. The downside is that for some carriers the texts may appear to come from an email address. Delivery is theoretically unreliable, especially outside the US, because most but not all providers have these email gateways.

As a result I would recommend Twilio for actual businesses, but Textbelt is great for personal stuff and other limited use cases. There are many businesses and monitoring solutions that use Textbelt though. It just depends on your needs.