NooDS is an open-source Nintendo DS emulator for Windows, Linux, macOS, Android, Nintendo Switch, PlayStation Vita.
The goal of NooDS is to be a fast and portable Nintendo DS emulator. It's not quite there speed-wise, but it does offer most other features that you might expect from a DS emulator. It even supports GBA backwards compatibility!.
NooDS doesn't provide high-level emulation of the BIOS yet, so you'll need to provide BIOS and firmware files dumped from your physical DS. The file paths can be configured in the settings. It also currently lacks automatic save type detection for DS games. If you load a new game and saving doesn't work, you'll have to manually change the save type. This information can be difficult to find, so it's easier if you have working save files already present.