Unison is similar to Outlook, with a full suite of e-mail, contacts, and calendar modes. Since Unison handles both messaging and telephony (VoIP), the software is presence-aware, able to switch your IM status when you are in a meeting or when you take a call.
I played with the demo and it's clear to me that Unison has about the same feature set (and even overall polish) as Outlook. Indeed, if you were in a hurry, you could easily confuse the two. On the other hand, seeing advertisements embedded in business-class e-mail software is disconcerting. Would you use a program like this for free, if the hidden cost was digital billboards on your desktop all day? Weigh in with your opinion in comments. [Via Techcrunch]