Windows/Mac: There are plenty of options if you want to control a Mac or Windows PC from another system, but Splashtop Remote Desktop is a new option that lets you start with a Mac and control other Macs or Windows systems, complete with HD video and graphics on the remote system.
The promise of full-screen HD video, gaming and remote control as though you were sitting at the remote computer is what makes Splashtop Remote Desktop stand out from similar, cheaper solutions like VNC. Splashtop does have the benefit of allowing you to manage both Macs and PCs from your Mac, but you'll have to install the Splashtop "Streamer", essentially a VNC server, on the client systems. Once installed, you can connect from your primary Mac and use those computers in a window, or full-screened, run remote applications, exchange and transfer files, and manage the system remotely.
Splashtop also offers a remote management app for iOS, Android and webOS that lets you manage systems from your smartphone or tablet. The Splashtop Desktop management app for Mac is available now at a launch price of $10.49 (it's regularly $20.99). If you want the mobile apps as well, they're available in their respective app stores for an additional $5.49 for phone versions and $10.49 for tablet versions. It's pricey, but if you prefer a company-backed and supported remote management system over building your own with free VNC apps, Splashtop can provide it.