First off, Convert Kit and Active Campaign are GREAT software (sorry AWeber and MailChimp). Using Convert Kit, I can definitely say it’s the simplest email automation software to use (that also doesn’t suck).
M. van Assem, V. Malaisé, A. Miles, and G. Schreiber. Proceedings of the Third European Semantic Web Conference (ESWC'06), volume 4011 of Lecture Notes in Computer Science, page 95--109. Budva and Montenegro, Springer-Verlag, (June 2006)