Sky3DS only plays .3DS ROMs. It acts like a cartridge game so no installing it onto the 3DS. So far it has been working on any firmware including 9.6. Good for those who can't run Gateway because of firmware updates.
31 game limit per mSD (recommend 32GB class 10 mSD and ROM-TOOL to trim ROMs). May have as many mSDs as you like. Works on Old3DSXL and New3DSXL. You will need private headers of original games to play Sky3DS online. We just figured out how to use Powersaves Pro dongle to rip headers out of OG carts and then use Sky Army Knife to fix the Sky3DS template file to use them. If you don't use private headers Nintendo can ban hammer you. So don't use Sky3DS with wifi on unless you have private headers on template file.
Even runs Cubic Ninja, Zelda-OOT for users who don't want to purchase carts so they can install or use Gateway.
Really handy tool. Even better thanks to [USER]Foxi4[/USER] who is working on the Sky Army Knife Tool.
So far, Sky3DS is the "easier" route to play 3DS ROMs. Gateway is still the only sysNAND backup and ROM dumper on the market unless you have NinjaHax on an old firmware.
DSTwoPlus should be released sometime soon, and there's lots of speculation on what it will do and how it will work. The old DSTwo has been discontinued.
And the KARL3DS team is working on an Open Source homebrew hack. Really neat stuff, but we're just drooling over it for now until they finally release it. Sadly, it won't support "piracy" or some sort of symantec debate of the likes.
Gateway does work on the New3DSXL system but requires Cubic Ninja or Zelda-OOT cartridges. Or a Sky3DS running CN or ZOOT. Have to run CN/ZOOT exploit every time you exit emuNAND.
Currently Gateway has not yet released the 9.6 emuNAND update. So everyone has lost access to their eShop. This also means no system transfers to new 3DS systems running Gateway until 9.6 emuNAND is out.
So Gateway if you can (sysNAND 9.2 or below). Sky3DS if you can't (sysNAND 9.3+). DSTwoPlus is still in shadows. Workarounds are everywhere.
a recommendation for you:
if you have a 3ds/3dsxl/2ds/new3ds/new3dsxl below or equal 9.2, buy a Gateway 3DS.
if you have 9.3 or newer, buy a sky3ds.
gateway is a more capable flashcart, sky3ds is the solution for the 3ds that does not have any exploit yet.
also, sky3ds it is a good complement to gateway if you do not wanna buy a cubic ninja/zelda oot and also if you want to have 2 3ds, one old3ds and one new3ds and the new one comes in 9.3+, in that way you can play old games in the old one and the new3ds specific ones in the new3ds but you will not have region free in n3ds so you only will use your regions specific game in that new3ds for now