Toraniko is a complete implementation of a risk model for quantitative and systematic trading. In particular, it is a characteristic factor model in the same vein as Barra and Axioma. It is basic but safe for production usage; in fact it is already being used in production at a systematic trading firm (>$2B GMV).
Using this library, you can create new custom factors and estimate their returns. From there you will be able to estimate a factor covariance matrix suitable for portfolio optimization with factor risk constraints (e.g. to main a market neutral portfolio).
The only dependencies are numpy and Polars. It supports market, sector and style factors; three styles are included: value, size and momentum. The functions you broadly want to have for constructing more style factors (or custom fundamental factors of any kind) are included.
A writeup that walks through (and motivates) the development of the library can be found in this X article: https://x.com/0xfdf/status/1808351541943763163