Cute 3DS Capture (C3C) is a 3DS capturing software for linux and Mac OS X for use with the capture boards by 3dscapture.com. It is written in C++ and uses SFML.
Install SFML and the SFML-headers (libsfml-dev or similar) as well as libusb-1.0.0 and the headers (libusb-1.0.0-dev). Then, simple do ./autogen.sh && ./configure && make.
Start Cute3DSCapture. You can autoresize the window with 1-0 (1x, 1.5x, 2x,... original size). Press the spacebar to toggle window split. Press C to toggle cropping to the original DS resolution (hold START or SELECT when launching a game)
If Cute3DSCapture doesn't detect your 3DS and you are using linux, copy 95-3dscapture.rules to /etc/udev/rules.d and reload udev-rules with udevadm control --reload-rules.
It was a play on words when I first tried to design a capture software for 3DS with Qt (which is prononced "cute"). Although I didn't stay with Qt, I liked the name Cute 3DS Capture and called the "port" for DS Cute DS Capture. Also, now I can call CDC and C3C (which is a very similar software but designed to work with a 3DS) "Cute Capture", if I refere to both of them.