Who uses Asterisk as the foundation for their solution?

I’ve seen multiple mentions of the fact that a lot of companies offering “unique” branded VoIP solutions, built their “proprietary” approach on Asterisk. For example, this quote from Digium CEO Mark Spencer:

“The impact of Asterisk would be hard to understate, as it forms the basis for countless free and paid PBX solutions.”

Where can I find a list of the companies who have done this? Does it include major players like RingCentral, 8x8, Jive, etc.