Colin Peterson submits:
USG Corp (USG) manufactures gypsum products: wallboard ("drywall"), joint compounds, and so forth. A wallboard panel consists of an inner core made of gypsum (calcium sulfate) plus various binders and additives, wrapped in paper.
Who else makes this stuff? Georgia Pacific, National Gypsum, Temple-Inland, CertainTeed (subsidiary of Saint-Gobain SA), PABCO Gypsum, Lafarge, and American Gypsum (once a subsidiary of Centex, now owned by Eagle Materials).