Ixion is an experimental formula engine library that can be used independently of the LibreOffice code base.
The repository for the Ixion library is found here https://gitlab.com/ixion/ixion.
Ixion integration strategy
Currently, integration of Ixion into LibreOffice code base as a replacement engine for Calc's current formula engine is put on hold indefinitely. However, we may use it in places where a light-weight formula parser and interpreter is necessary.