I've got a customer who has 40 users on Office 365 E1, recently transitioned from BPOS. Right now they don't have an on-premises server at all; therefore, no AD - just workgroup with a QNAP NAS.
To make it easier for employees to access all their mission-critical applications in the cloud, many enterprises are turning to single sign-on solutions, the most popular of which is Microsoft (News - ...