All chat platforms (that I can remember) that were popular around that time used proprietary protocols, including ICQ. Everyone I knew preferred third-party clients to the official one, and these clients would sometimes break because ICQ kept changing tiny details in the protocol to try to force users to use the official client. It never worked, of course, because updates that fixed compatibility would usually come within a couple of hours.
I guess not open open, but at least they weren't behind cryptographic walls.
It is an embarassment that in 2024 you still can't send someone an iMessage from a PC or Android phone. Shoot, messaging from a PC in general is hard. No easy SMS access, and even third party apps often have stupid things like "the app is actually running on your phone but you can forward message to some flaky and bloated electron thing on a PC if you really must."
