[51Cards]

I still use Trillian just for the UI. I can have several chat windows open along the top of my screen without taking up much of my working space. Since I work remotely from most of my colleagues this is priceless and I don't know what I'll do when I am forced to switch. I was also a heavy ICQ user from the 90's into the early 2000's for all the reasons you cited.

[flud]

Does Trillian support slack by any chance?

[51Cards]

Pasting this reply I found elsewhere. Should be accurate to my knowledge.

Yes to Slack! Ask whoever manages your organization to enable XMPP or IRC gateway connection, then add the appropriate type of account to Trillian. You won't have access to rich cards or shared files from within Trillian, but you will be able to read and send messages to channels and individuals.