You can download a trial install of the latest version of Sametime.
Lotus Sametime is IBM's instant messaging software, but it has grown a lot in this release to become a real-time collaboration platform for co-workers; see What's new at a glance?. I'd never used Sametime before joining IBM, but I've been using beta versions of 7.5.x for about six months now and it blows the doors off of any instant messaging I've used before. You can download the Sametime v7.5.1 trial from developerWorks.
Trial: IBM Lotus Sametime V7.5.1