Camunda - The Universal Process Orchestrator
Google App Engine - A powerful platform to build web and mobile apps that scale automatically.
ProcessMaker - ProcessMaker is an easy to use BPM and workflow software solution. It is used to design, automate, and deploy business processes of any kind.
Dokku - Docker powered mini-Heroku in around 100 lines of Bash
jBPM - jBPM is a flexible Business Process Management (BPM) Suite.
Google Cloud Functions - A serverless platform for building event-based microservices.