Zentyal was mentioned in the FreeNAS 10 Beta 2 announcement. It’s a Linux Active Directory and Exchange server appliance. Granted, if you’re going to use Exchange for email you should buy an Office 365 subscription and let Microsoft deal with hosting it but overall this is a very interesting project. I’m making note of it for personal reference more than anything.
BTW, if you need a NAS or SAN then you really ought to look at FreeNAS. I rolled my own at home and we bought a box from iX Systems (sponsor of the FreeNAS project) at work. The FreeNAS Mini is a nicer equivalent to what I built. The FreeNAS Mini XL is its big brother. Both are ideal for home and maybe small business users. Don’t bother with the read and write cache upgrade options, just get as much RAM as you can afford and consider the 10Gbps Ethernet upgrade.