YQL Auto Tagger
The plugin performs an analysis of your post text and suggests tags for you.
Plugin Tag: semantic web
WP Calais Archive Tagger
Goes through your archives and adds tags to your posts based on semantic analysis.
Semantic Tags
Semantic Tags plugin provides you everything you need to create and semantically markup your Tags.
wp-linked-data
Publishes blog post & author data as Linked Data.
JSONLD Semantic Tags
Semantic Tags plugin provides you everything you need to create and semantically markup your Tags.