Windows/Mac/Linux: InstantBird is an instant messaging client that looks great and won't drain system resources. If you want a highly customisable IM application that provides a consistent experience across Windows, Mac OS and Linux, it's worth a try.It's been a while since we last mentioned InstantBird, but the 1.0 release is a big improvement. The developers of InstantBird will be the first to tell you that it's not the most feature-rich application, but what it lacks in native features it makes up for in add-ons and themes contributed by the user community.
The new version of InstantBird is inspired by the clean look of Pidgin (and actually uses its libpurple protocol library) but the UI is a bit more attractive. Plus, it's free. For alternatives, check out our picks for best instant messaging app for Mac and for Windows.