These are sites which have been discovered and are being used by millions, and which have in common characteristics of LowCostOfEntry?, HighParticipationLevels?, EasyToUse?, available on many ComputingDevices?. They also are found to be light in content, or heavy in it, depending upon the user. Most are UserNamePassword entered for personal use.
Examples:
Most of them are accessible on mobile devices via what has been simply call apps. To make it a WikiWord I call the IconicApps?, since they are often accessed in a single touch on the representative icon for the app.
The sites mentioned above and many more are becoming the BackChannel of communication, where people are physically present but are ComputationallyWired?.