ThinVNC is a remote desktop tool that makes it easy to access a remote PC over the internet.
As with most of the competition, you first download and install a server on the Windows PC you'd like to access (the program supports everything from Windows 2000 upwards).
Unusually, though, you won't need a client to connect to the system. ThinVNC is what the authors call a "pure-web Remote Desktop solution": you'll be able to access your system from any convenient system, anywhere in the world, just as long as it has an HTML5-compliant browser (Firefox, Chrome, Safari, maybe IE9).
This does introduce some complications. Internet Explorer is still the most commonly installed browser by a considerable margin, and so if, say, your work PC has IE8, then you won't be able to use ThinVNC to access your home system without installing a more HTML5-friendly alternative.
Still, the "pure-web" approach does mean you'll be able to see your Windows desktop, and run its programs, from a Mac or Linux system, as well as other Windows computers.
And this is a real plus point for ThinVNC's Presentation Mode, which allows you to securely invite people to your PC, and show them what's happening on your desktop, or selected applications, great if you need to collaborate with others at a distance.
Please note, ThinVNC is free for non-commercial use only. Licences are available for commercial use, with prices starting at $20 per seat, and you can find out more at the ThinVNC site.
ThinVNC is straightforward and easy to use, but the HTML5 requirement may be an occasional hassle