nullDC will not disappoint you. It runs on Microsoft Windows terminals and emulates Sega Dreamcast and NAOMI. It came out with a MIT license, with the latest version being released in 2011. The emulator comes with a few requirements. For example, you need DirectX, Visual C++ libraries and WinPcap for certain applications. BIOS files will also be required. While abandoned, the emulator is still widely popular among gamers because of its high accuracy and smooth operation. ROM images are easy to find too, yet none of them is included in the package due to copyright issues.
A more recent version of nullDC has hit the market under a different name – specifically designed for Android. It was not as successful as developers expected. As for games, you can now enjoy Crazy Taxi, Sonic Adventure, Jet Set Radio and Skies of Arcadia – among other old fashioned games – on your personal computer.