ObservePoint - Monitor, test and validate the accuracy of your web tags, critical user paths and more with ObservePoint's automated Data Quality Assurance solution.
Dia - Dia is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license.
Hub'Scan - Hub’Scan is an SaaS platform that performs web analytics tag audits and validates tagging plans & certifies banner ad campaigns.
draw.io - Online diagramming application
Tag Inspector - Tag Inspector is a marketing tag auditing and alerting tool that empowers its clients to report on web analytics tags.
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.