Knoodl is sort of an ontology editor, registry/repository, and wiki all rolled into an easy to use online application. There's never been anything quite like it.

* Upload an ontology you already have, or build one from scratch.
* Add rich documentation with wikitext, so that other people can understand what your ontology is about.
* Work with other people on the same vocabulary, at the same time
* Find and download other ontologies and use them in semantic applications.