Acapela is... a-cape-for-Bela (http://bela.io/), and a box.
It is composed of two things, a circuit board and a box (or enclosure). The circuit board has space for eight potentiometers and two 1/8" TRS (a.k.a. Jack) connectors for stereo audio input/output. It attaches directly on top of Bela. The box just keeps everything together and makes it easier to move around.
I decided to build Acapela to be able to prototype and test my audio programs with Bela in a more portable way anywhere (e.g. on the tiny tables of my favourite coffee house, on the train going to work, etc.) and to avoid carrying hairy circuits made on a breadboard with jumper cables and noisy sensors that disconnect easily. The potentiometers in Acapela can simulate any sensor to be replaced later on a specific product, or they can just be the controls of the final product (e.g. a guitar pedal, a synth).