Update: It appears RDGateway support is currently in the release client, so we're not sure what this beta update actually added.
Microsoft's RDP client for Android is a surprisingly robust application, and today the beta version just got a pretty significant new feature for corporate and enterprise users: Remote Desktop Gateway support.
RD Gateways are servers that allow remote desktop clients to start a remote desktop session from outside the corporate intranet via an SSL-encrypted port, meaning you don't have to use a workaround like a VPN connection. They're common enough in corporate and enterprise environments, so if you're curious, maybe ask your IT guy (assuming you aren't the IT guy).
Microsoft is also teasing new features coming in future updates to the beta, including support for Remote Resources (see this primer in the iOS version here) and Azure RemoteApp (kind of Microsoft's Citrix Receiver, I think).