FreePBX (built on Asterisk, which is the basis for another dozen PBX platforms) is still far-and-away the most popular PBX platform for small businesses and most VARs. FreeSWITCH does exist and it is fantastic, but the two are quite similar in terms of what they can accomplish.

There is really no other option in the FOSS community for small-to-medium phone systems, as Asterisk-based systems are rivaled mainly by 3CX (proprietary) in the industry which is somewhat expensive and significantly less-configurable than the open source options.