Tools

• Protege – the editor for ontologies.  http://protege.stanford.edu 
• Robot – a command line tool for processing ontology files – merge, extract, diff, and more http://github.com/ontodev/robot 
• easyRDF converter – http://easyrdf.org/converter converts RDF files to and from various formats – N3, NT, Turtle, RDF/XML

To Read

Here are two great resources that everyone working with ontologies should read:

• Building Ontologies with Basic Formal Ontology  https://goo.gl/zE6SHh
• Semantic Web for the Working Ontologist  https://goo.gl/c8jfpf 

More Resources