The mGBA emulator is available on multiple platforms.
Again, while we can’t recommend any particular sites, there are websites that will emulate GBA games within your web browser, so you won’t need to find or download any of these games yourself. If you’re unwilling to take the risk, you can also consider playing GBA games online. You should also double-check the piracy laws for your country before you proceed. If you decide to download GBA ROMs online, check the files thoroughly for any potential malware infection before opening them. Several online sites do exist that offer GBA ROMs (as the game files are called) for download, but you’ll have to find these yourself. With that in mind, it isn’t possible for us to provide information on where you can find your own Game Boy Advance games for download.