In the computer science fields of knowledge engineering and ontology, the Sigma knowledge engineering environment (SigmaKEE) is an open source computer program for the development of formal ontologies.

The user's typical workflow consists of writing the theory content in a text editor and then debugging it using the SigmaKEE's tools.

The interface allows the user to make queries and statements in SUO-KIF format and shows proof results with hyperlinks.

The interface allows to browse the theory content with hyperlinks and presents hierarchies in a tree-like structure.

The theorem prover E, which supports TPTP standards for input and output, is integrated into SigmaKEE.