LogMeIn offers software to remotely control a Mac from another Mac, Windows, or Linux PC. It also introduces software-as-a-service support so that a technician can remotely perform diagnostics and repair operations on a Mac.

An excerpt from News.com:

Both new LogMeIn tools work with Macs running OS 10. 4 Tiger and 10.5 Leopard operating systems. Users can access their Macs from browsers on computers running Windows, Mac, and Linux operating systems, as well as on the iPhone and other compatible handhelds.

Both LogMeIn Free and LogMeIn Rescue are free downloads. Both the products are browser-based.

More information:

LogMeIn’s remote access tools now on Mac (iTWire)

Third Parties Support Mac in the Enterprise (eWeek)

LogMeIn extends Mac remote control support (VNUnet)