For power users, access to Windows is possible thanks to the excellent VNC Viewer app from RealVNC. Users run VNC Server on their PC and use VNC Viewer to connect remotely. It really works, and shows just how powerful a browser UI can be. This is a photo showing Internet Explorer running on the HP Pavillion Chromebook using the VNC Viewer app. We were able to access the VPN, and corporate applications, even though Chromebooks are not supported devices.
For IT admins there is also an SSH client app, which can be used to connect into Linux and Unix server. And VDI access is supported through Citrix Receiver app.