The OWL API is a Java API and reference implmentation for creating, manipulating and serialising OWL Ontologies. The latest version of the API is focused towards OWL 2
Welcome to the OpenMath website. OpenMath is an extensible standard for representing the semantics of mathematical objects. If you haven't heard about it before you might want to consult the overview.
S. Auer, C. Bizer, G. Kobilarov, J. Lehmann, R. Cyganiak, and Z. Ives. Proceedings of the 6th International Semantic Web Conference (ISWC), volume 4825 of Lecture Notes in Computer Science, page 722--735. Springer, (2008)
Y. Yang, and J. Calmet. CIMCA '05: Proceedings of the International Conference on Computational Intelligence for Modelling, Control and Automation and International Conference on Intelligent Agents, Web Technologies and Internet Commerce Vol-1 (CIMCA-IAWTIC'06), page 457--463. Washington, DC, USA, IEEE Computer Society, (2005)
J. Breslin, A. Harth, U. Bojars, and S. Decker. European Semantic Web Conference (ESWC), volume 3532 of Lecture Notes on Computer Science, page 500-514. Springer, (2005)
T. Gruber, and G. Olsen. Principles of Knowledge Representation and Reasoning: Proceedings of the 4th International Conference (KR '94): Bonn, Germany: 1994, May, 24 - 27, page 258-269. Morgan Kaufmann Publishers, (1994)
V. Uren, E. Motta, M. Dzbor, and P. Cimiano. K-CAP '05: Proceedings of the 3rd international conference on Knowledge capture, page 75--82. New York, NY, USA, ACM, (2005)
B. Grau, I. Horrocks, Y. Kazakov, and U. Sattler. IJCAI'07: Proceedings of the 20th international joint conference on Artifical intelligence, page 298--303. San Francisco, CA, USA, Morgan Kaufmann Publishers Inc., (2007)