Customer.io Newsletter is Customer.io's product line for email and message automation, founded in 2012 in Portland, USA, using an event-driven engine and visual customer journeys to send personalized emails and push based on real user behavior.
ActiveCampaign Newsletter is ActiveCampaign's email marketing product line, founded in 2003 in Chicago, USA, combining visual automation workflows, behavior triggers, and multichannel reach for 180K+ business customers.
Mautic is an open-source marketing automation platform launched in 2013, GPL-licensed and self-hostable, serving 200,000+ users with email marketing, lead scoring, and customer journeys.