No$GBA is a relatively new emulator, one version of the No$ proprietary emulators. No$ emulators were developed by Martin Korth, and No$GBA is the version that emulates GBA, Nintendo DS, and Pocketstation. No$GBA is not to be confused with any other No$ emulator, which is all for different systems.
No$GBA is one of the best-reviewed and most trusted of all the emulators due to its ease of use, and the fact that there are no requirements to run it, with no requirement to install new cores or any third party tool. Simply by placing the ROM file into the appropriate folder, changing its name to what you want, and reloading it, you can be gaming straight away. Initially No$GBA was just a Nintendo debugger, yet has since developed into the full-fledged emulator it is today. As a result of this history, it has by far the best debugging features out of any emulator on the market, as all its original debugging features were retained. What makes No$GBA so attractive to those who like to customize their emulators, is the extensive documentation provided by Martin Korth, who explains in depth how the emulator works, allowing others to edit it as they please. So despite being a proprietary emulator, it is actually popular in the emulator customization subculture, the same as an open source emulator might be.