Imo supports /ICQ, Facebook, Google Talk, Jabber, MSN, MySpace, , and Yahoo. You can choose to link your accounts, so that you sign into all of them simultaneously with just one login. Once you sign in, imo displays a list of your contacts on the right side of the screen, with a small icon indicating which service they are using. You can change your buddies' aliases if you'd like to identify them more easily, but you can't merge contacts. This is unfortunate, as many of my AIM buddies also are my Skype contacts and my Facebook friends. If I could merge them, I could clean up my unwieldy contact list, and make a faster decision on how to contact them.
You can choose between a window view, where new conversations are shown in traditional, IM-like boxes on imo's main screen, or a tabbed view, where conversations are organized into different tabs. The window view works well if you're managing only one or two conversations, but can be overrun if you're chatting with more folks. That's when switching to the tabbed view (which can be done by clicking an icon) makes sense.
I like that you can set imo to save your chat history, as too many clients make it easy to delete valuable information when you close a chat window too quickly. You can save these indefinitely, and can delete individual conversations if desired.I also like how easy it is to send voice IMs. If you want to send a voice message, you can record one that's up to 30 seconds long and send it to any of your contacts. Imo says the messages are playable on most clients, and my AIM contact was able to receive it without a problem.
You can conduct a voice or video chats with any of your contacts, no matter what IM service they use, as long as they have speakers, a microphone (or a headset), and a Webcam. If their IM service doesn't support voice or video chat, imo sends a link to an HTML-based voice/video chat window that doesn't require a login. You can send files to, and receive them from, other imo users; you can also send them to non-imo users, but can't receive them.
Imo has plenty of useful features, but it's not without flaws. In my tests, I occasionally experienced network outages that left me unable to chat, albeit briefly. I also noticed that the service didn't display images for all of my contacts. It displayed Facebook profile pictures for only about a quarter of my contacts, but not for the rest of them. These issues are minor, and are not enough to detract from imo's appeal.