You might find this recent white paper of interest...
Journal of Object Technology, vol. 14, no. 1, 2015,
Evaluating the capabilities of Enterprise Architecture modeling tools for Visual Analysis
Department of Systems and Computing Engineering, Universidad de los Andes, Colombia
Open Source Diagramming / Architecture Tools...
Not sure about these...haven't spent any time exploring them yet...
I've found Graphviz to be useful for automating diagram generation from any available metadata sources...
...but today, I would look at adopting D3.js - for some stunning diagramming capabilities...
SchemaSpy is a great tool for auto-generating HTML documentation of existing database schemas - and it leverages graphviz behind the scenes to auto-generate diagrams...
this appears to be a more actively maintained type of database schema doc tool..
There are some useful plugins available within the Eclipse ecosystem - and the latest version of Eclipse (4.6, Neon) was just recently released
The plugins that I've found useful:
Some examples, specific to modeling efforts:
Diagramming tooling...some are Open Source...some are free (or have limited-use restrictions) - some have UML/Archimate/etc. support...