If you're like me, you like free software. Not free as in "download this and we'll take over your computer" free, or "download for free but we're going to annoy you with ads and popups to tell you to purchase the full version" free, but free as in "we made this program, here's the source code, if you want to improve on it, do it" free.
Miranda IM is an instant messaging multi-client. What that means is that if you run Yahoo IM, AIM, MSN, IRC, ICQ, or many other instant messaging protcals (more than 1 at a time), this program can do it all.
Right now I have all 5 of the above running under this 1 program, and I can see all of my contacts from those appications, rename them, customize them, everything. Running all 5 of those applications at the same time would eat up my system resources and make my computer slow, but with Miranda IM, as it's just 1 program, it's taking up very little memory. This is because it cuts out all of the unnecessary stuff that all the other programs have (advertisements, bloated features that no one ever uses) and has just what people run. If you do run one of the features that were cut out, you can get a plug-in to add the feature, all while still keeping its slim features.
Customization is a little difficult, but with it, you can make an amazing looking application that will make your friends ask "Wow, what is that?"
The biggest problem this program has, though, is that it's constantly under development. While updates are frequent, some problems arise that require someone to fix it. Luckily, there's a large community behind Miranda IM, and they help create features and bug fixes that benefit the program.
If you run more than 1 messaging program, look at getting Miranda IM. It'll cut down all the "bloat", and you can customize it to match your personality (or computer theme). Definitely worth checking out.
Did I forget to mention that it's free?