In a previous (now deleted post), @normis did mention all of PPPoE, PPTP, L2TP, SSTP, OpenVPN.
As for the "server/client" or only "server" or only "client" part: If we trust this statement:
then we can probably exclude anything "client" because the use of PPPoE client is very common for home user configs (it's one of the supported QuickSet options). Logic dictates that only the "server" part is affected.