Coding can be done in C-style language with the Arduino IDE.
Python API for sending serial commands
Bittle can be programmed with a Scratch-like web-based IDE Codecraft and curriculum
The Code & Robots iOS app can control a few open source Robots, include Bittle.
Please check out the following video for the app configuration to support controlling Bittle.
Inverse Kinematic Model OpenCat
a discussion thread
OpenCatWeb - a web interface to control Opencat-based robots
need to mount a Raspberry Pi
a discussion thread by the author leukipp