I am a big fan of small and simple yet practically interesting ideas, like this one. CurlMail is a super easy API service that allows one to send emails from the command line, using nothing but curl, or a similar HTTP client.
It’d be extra cool if it there was a GitHub link to it too. But even if it’s not openly available, one could use the service for emails which are not sensitive and implement something similar from scratch in a few minutes for private use.