ArcadeVGA is a video card, that was made specifically for Windows, that allows people to use an old arcade monitor, typically using a 15Khz signal.
Most modern PC video cards output a 31Khz or higher signal, which is incompatible and in some cases harmful to real arcade monitors. As video cards evolved, 15Khz signals were abandoned by card manufacturers as they were no longer used by modern SVGA monitors. This can make it difficult to get standard video cards to display correctly on an arcade monitor.
ArcadeVGA supports many arcade resolutions used by MAMEtm and other emulators, so you don't need any software scaling in most games. This results in games being displayed on your arcade monitor exactly as they were originally intended.
Some resolutions used by certain games may not work on your arcade monitor, so these may need to be disabled with a resolution tool.
There is now an updated version of the ArcadeVGA, the ArcadeVGA 2. Available in both AGP (based off the ATI Radeon 9250 chipset) and PCIe (based off the ATI Radeon X550, with 512mb of video memory) the ArcadeVGA 2 is capable of, along with the original 15khz resolutions, 25khz resolutions as well as PC resolutions up to and including XGA (1024x768). Additionally, it has dual outputs (one VGA, the other DVI - as well as S-Video, though this output isn't recommended by Ultimarc) which, along with the drivers on the accompanying disc, enable simultaneous dual-monitor support (though, the ports are specific: VGA port strictly for arcade monitors, DVI port for PC monitors).