In the case of "Open Source", that seems to be readily explainable by it being either an adjective or a noun, with the adjective being lower case and the noun b

In the case of "Open Source", that seems to be readily explainable by it being either an adjective or a noun, with the adjective being lower case and the noun being proper. "Internet" fits with that; you might say that an internet service provider provides access to the Internet (or, someday, to one or more internets, once there's really no longer a single Internet).