Complex sentence: Advocates of free and open source software refer to free or open source Java virtual machine software as free runtimes or free Java runtimes Until November 2006, this was contrasted with the proprietary nature of Sun Microsystems' "Java runtime" offerings.
Split into simpler sentences: Advocates of free and open source software refer to free or open source Java virtual machine software as free runtimes or free Java runtimes. This is contrasted with the proprietary nature of Sun Microsystems' "Java runtime" offerings.