which of these were a way to send money through a social network's chat client?

SnapCash and SquareCash are one & the same. I think it's a great convenience to add CC to my FB, but since I do not use a real name, do not trust FB, and would be concerned about my account being compromised (though it probably makes you enter a CSC/PIN), I will not be using this any time in the near future.

I personally use SquareCash all the time, and also use PNC bank's complimentary POPmoney setup to transfer funds for free (with PNC, I scheduled a partial rent payment to go to my landlord's bank account automatically every paycheck).