TopBraid Composer is an enterprise-class Semantic Web modeling and application development environment.
There is a Free Edition that provides an Eclipse-based editing and querying tool for RDF and OWL files. In addition to form-based editing of classes, properties and individuals, the Free Edition also has comprehensive SPARQL support, including the SPARQL Inferencing Notation (SPIN) http://spinrdf.org. SPIN can be used to define highly expressive business rules and constraints on domain models, entirely based on SPARQL using an open source API based on Jena ARQ.
TopBraid Composer uses Jena under the hood and has an open API for developing plugins.
The Free Edition has a subset of the features available in the Standard and Maestro commercial products.
SPARQL Web Pages
TopBraid Composer 3.4+ provides support for SPARQL Web Pages which render Semantic Web data. The SPARQL Web Pages - User Guide and SPARQL Web Pages Support in TopBraid provide a starting point for using SPARQL Web Pages in TopBraid Composer.