Today, we would much rather IM that call, text or simply meet people. We like it that way, talks never get awkward, you have excuses of saying stuff like you were busy and did not check etc. But, what is also true is that we have a million and a half IM accounts too. For those working, they always have a work IM to go with personal one and more. This is where you need a multi platform, all in one sort of a solution.
For those on Mac OSX, the best solution bar any is Adium. Yes, I know there is Jabber which does the same job, but jabber has always been very hit and miss for me. It skips notifications and things like adding friends is always an issue. Adium, being free and highly customizable is a fantastic thing to fall back on. You can pretty much control unlimited accounts using it from Gmail to Yahoo to Facebook to even AIM.
You have the options of playing around with the notification types, the chat bubbles, fonts, windows etc. Basically, everything in the app is extremely customizable, and above all, all this and so much more for a free and open sourced app so you can always think, a lot more will be added to the application. I have been using the app personally for a solid while now and another thing that has really impressed me is the fact that it is extremely easy on the memory. So, if you are looking for an all in one messenger app, Adium is surely your best best for Mac OSX.
You can download the app from here.