Notice: This software is in a transiton stage: lots of unnecessary code have already been thrown out, and more to follow. There will be renamimgs. This means - among other things - that model files will be incompatible with other versions for a while.
Zenta is a free, open source, cross-platform tool and editor to create models along with their metamodels.
Zenta is forked from Archi, which is an implementation for the Archimate methodology. Archimate is a closed standard of the Open Group. Yeah! This created a situation where in theory you could use a software with an expressed open source licence only with permission. And anyway, you might want to use other - or more - metamodels.
Zenta is targeted toward all levels of Architects and Modellers. It is intended to provide a low cost to entry (i.e. free) solution to users who may be making their first steps in the architecture modelling or who are looking for a cross-platform modelling tool for their company or institution.
Zenta boasts an export module which can export your model theoretically in any format, and does have styles to do it in docbook, html, opendoc and csv.
The export module also does conformance checks to your metamodels.
Metamodels are easily expressed with graphical models.