DSES is a simple tool to set the EULAs for the 3DS to accepted.
In order to play 3DS games online/make use of streetpass, the 3DS makes the user accept an EULA. If this is for in-region titles, this is can be handled by the 3DS itself. If you wish to make use of out-of-region titles however, you will need to use homebrew to set the EULA to accepted.
A number of EULA setting tools exist already (notably, SciresM/EULASetter, which is the base for this tool).
However, all of these tools I've encountered so far sometimes offer a lot of other features and more importantly, put hex values in front of the user.
This tool does none of that. It does one thing. Set your EULA to accepted if it isn't and to unaccepted if it is. No complications, nothing. Just press A and it changes the EULA.
Note that when unaccepting the EULA, you will need to reaccept it the next time you use a 3DS game in your own region.
Download the CIA from the releases page and open it with FBI. Press A to change your EULA. Press SELECT to remove the program after running it.
If for whatever reason you need to reset the EULA to its initial values, rerun the application again.
There is also a 3DSX option available for those who prefer 3DSX homebrew. Put it on your SD card and run it with the Homebrew Launcher or with 3dslink. Press SELECT to remove the program after running it.