DRVgraph - Defeasible Logic Rule Base Visualization with d-graphs:

DRVgraph is a defeasible logic rule base visualization framework, based on Nute's defeasible logic graphs (d-graphs).

S2REd - Syntactic-Semantic RuleML Editor:

S2REd is a text-based RuleML editor that features semantic tag mapping for the domain specific RuleML tags. Developed by Thetida Zetta.

RDFViz++ - Graph-based RDF Visualization:

RDFViz++ is an RDF visualizer that combines 3 visualization techniques (display-at-once, navigational-centric, centric-graph-at-once) into one alternative visualization approach, leveraging the drawbacks by other available tools! Developed by Aris Athanassiades.