Scalr - Scalr is cloud management software for public & private infrastructure
Dia - Dia is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license.
Mist - Mist is a Multi-Cloud Management Platform - Streamline operations + Optimize costs across public & private clouds, hypervisors & containers.
draw.io - Online diagramming application
Stackmasters Managed Cloud - Stackmasters provides cloud management and application hosting solutions for private, public and hybrid clouds.
yEd - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.