The unique feature is:a) the inter-operability between and...

The unique feature is:

a) the inter-operability between and across platforms, that is being able to call, conference and transfer across multiple platforms, e.g. Skype, Hangouts, Messenger, WhatsApp, Landline, Mobile,... all those other items you mention are intrinsic to the individual platforms and have been around for year, but all users have to be on the one platform, e.g. to have a Hangouts conference call all call participants need to have a Hangout account and call in to join the conference via Hangouts

b) the ability to call a "contact" have the call ring on all contact platforms, that is for example their mobile phone, their house phone, their office phone, their Skype, their Whatsapp,.... (instead of current technology, you ring Fred on his mobile, no answer, you try him on skype, no answr, you try him at the office, finally an answer...)