It's a simple shim library that should allow you to play sf2d homebrew games on your PC.
It also provides "emulation" for some functions provided by ctrulib.
Obviously, the game in question needs to have its source code available so it can be recompiled.
The library was tested against Memory3DS, a 3DS homebrew game by Omegadrien.
Memory3DS works quite well using this library.
This however isn't the case for all the other homebrew games... (like Minicraft3DS for example)
Some functions were also taken in part or directly from ctruilib and sf2dlib :
crtuilib has no license (i assume public domain ?) and sf2dlib is under the MIT license, copyright Sergi Granell (xerpi).
Updates It looks like sf2d got deprecated in favor of crtui3D. As a result, this thing is pretty much useless now. Besides, it's not like people released the source code to their 3DS homebrew games...
Pray so that your games in question does not use low-level GPU functions or else it will not work properly. (only stubs for now and it's not the focus of this)
Text is not displayed properly because SDL_ttf doesn't allow to change the size of a text without closing/open a new font again.
Lots of functions are either stubs or are only partially supported (like rotations for rectangles).
For now, you cannot load an image from a C array. (use the PNG loader)