AnyLogic - AnyLogic has changed simulation modeling and expanded its application into complex business environments. The unmatched flexibility of multimethod modeling allows users to capture the complexity of virtually any system, at any level of detail.
Google App Engine - A powerful platform to build web and mobile apps that scale automatically.
ns-3 - a discrete-event network simulator for internet systems
Dokku - Docker powered mini-Heroku in around 100 lines of Bash
Paessler Multi Server Simulator - Paessler Multi Server Simulator is inexpensive and robust software that helps you power massive-scale testing.
Google Cloud Functions - A serverless platform for building event-based microservices.