Hi,
The app is called Messages.
The Main account in High Sierra is the iMessages one.
The version is called version 13.
However 1 to 6 were iChat versions that ended in Lion (OS X 10.7.x)
By that time the app had gone from being an AIM Client with a Bonjour account as well to having Jabber and Yahoo abilities as well.
Yahoo was text only and stopped around Yosemite as well
AS has been stated Google Talk used a Jabber server (So did Facebook for a while)
Yahoo closed their Yahoo app and rewrote it which is why the Mac Messages version no longer connected.
AIM have stopped Client apps connecting and will be discontinuing the service as a whole in December (A long standing agreement with AIM used to Allow Apple Issued Apple IDs to be valid AIM Screen Names (@Mac.com @me.com if linked to iCloud and @iCloud.com IDs) )
Bonjour also present for Mac to Mac connections on the same LAN has also disappeared in the High Sierra version.
A Google ID in System Preferences > Internet accounts used to have a Messages option that you could turn on as well but in High Sierra you have to set up a separate Messages account in Internet Accounts.
9:39 pm Monday; November 13, 2017
iMac 2.5Ghz i5 2011 (Sierra)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
iPhone 6 iOS 11.x and an iPad (2)
