This is a rewritten firmware for the "Sparmatic Comet" and "Sparmatic Zero V2" electronic heating thermostats. They have been marketed cheap in some German supermarket chains years ago. They are based on an ATmega169 controller, a custom LCD glass, and a motor to operate the valve. A simple menu system, arranged around three buttons and a thumbwheel, complete the system.
There is a lengthy thread in the (German) mikrocontroller.net forum dealing with all the details of these devices:
https://www.mikrocontroller.net/topic/237375)
https://www.mikrocontroller.net/topic/237375?page=1#2407844 contains links to schematics and photos of the device.
Wiki page with many details (in German language):
https://www.mikrocontroller.net/articles/Sparmatic_Heizungsthermostate
This project is a complete firmware rewrite. Knut Ballhause provided assembly code rewrites which are licensed as Public Domain (CC0), and are available in the directories Sparmatic_Comet_M169_AVR5/ and Sparmatic_V3_Thermostat_M169PA_ATM6/.
The subdirectory C/ contains a rewrite of Knut's assembly code in C. Originally, the goal of the rewrite was to produce a bug-to-bug compatible C counterpart for the assembly code, and it has been worked on from that. This code is by Jörg Wunsch, and is also licensed as Public Domain.