Google App Engine - A powerful platform to build web and mobile apps that scale automatically.
Paessler Multi Server Simulator - Paessler Multi Server Simulator is inexpensive and robust software that helps you power massive-scale testing.
Dokku - Docker powered mini-Heroku in around 100 lines of Bash
ns-3 - a discrete-event network simulator for internet systems
Google Cloud Functions - A serverless platform for building event-based microservices.
FlexSim - Simulation software to model, simulate, predict, and visualize systems in manufacturing, material handling, healthcare, warehousing, mining, etc.