Mautic is the most popular open-source automation software. It is used by over 200.000 organisations around the world. It is battle-tested and feature-rich. It allows companies to use 21 century marketing tools, keeping the whole process in house and owning all of the data. Personalisation and campaign management are easy with Mautic, but so is GDPR compliance.
If you are looking for an extendible and flexible Marketing Automation Package, you should give Mautic a try!