The Arborator software is aimed at collaboratively annotating dependency corpora.
Please simply try it out on the 
access to the Arborator (no login is needed)!
Click on the Help link on top to understand the features.
The quick page allows to easily
- visualize and edit a CoNLL file of dependency annotation
- create a dependency graph for a yet unannotated sentence
- export in graphical or CoNLL formats.
A report on Arborator's options for class-sourcing dependency annotation is here: https://scholar.google.fr/citations?view_op=view_citation&hl=en&citation_for_view=jCFpJfEAAAAJ:k_IJM867U9cC
Please also cite this article if you use Arborator for research.
Check out the instructions on the Wiki page.