Kiva is a free and open source ground heat transfer calculation tool written in C++. Specifically, Kiva is used to calculate heat loss and gain on a timestep basis from building foundations. The goal is to create a tool that can integrate the multi-dimensional heat transfer into standard building energy simulation engines.
Kiva has been integrated into the EnergyPlus whole building simulation engine. More integrations are in the works.
getting-started input-def/index methodology testing bibliography