There is only one alternative loader that is known period, and that is YSMenu. Apart from that, any other loader is just a homebrew loader. With that said, ANY alternative firmware you put on your flashcart will be using ysmenu to load commercial roms (so be sure you can install it correctly first xD).
As for alternative GUIs, I recommend Xenon++'s WAIO or Moonshell2 since I like both of them xD.