TeamViewer is a screen sharing, remote control and collaboration tool connecting devices for troubleshooting, presentations or installations. Supports standard chat, high-quality voice and video, file transfer, whiteboard, session recording, remote printing, screen sharing and more. The program can work with paranoid firewalls, functions as a VPN between clients, will display quality based on connection speed and includes browser access.
Clients are also available for Mac, Linux, iOS, ChromeOS/Android and more with support for many world languages.
Alternatively, a PortableApps version is also available: TeamViewer Portable.