Jasmin SMS Gateway - Jasmin is a very complete open source SMS Gateway with many enterprise-class features such as:
Brevo - Innovative online Email Marketing solution to manage your contacts, create & send your newsletters and track your results. More than 80 000 clients. Best prices and attractive features.
Kannel - Open Source WAP and SMS Gateway
MailChimp - MailChimp is the best way to design, send, and share email newsletters.
Ozeki NG SMS Gateway - Ozeki NG SMS Gateway is a powerful, reliable and flexible SMS Gateway application.
SendPulse - Maximizing e-mail marketing open rates automatically