Grafana - Data visualization & Monitoring with support for Graphite, InfluxDB, Prometheus, Elasticsearch and many more databases
Dia - Dia is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license.
Mozaik - Mozaïk is a tool based on nodejs / react / d3 / stylus to easily craft beautiful dashboards.
draw.io - Online diagramming application
Dashing.io - The exceptionally handsome dashboard framework
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.