QuantLib – Open-Source Quantitative Finance Library
by QuantLib Project
Industry-grade open-source tools for yield curve modeling, MBS prepayment models, and interest rate derivatives.
More resources on Excel for Finance
Simtools – Free Monte Carlo Simulation Add-in for Excel
Free Monte Carlo simulation and statistical functions Excel add-in created by Nobel laureate Roger Myerson at the University of Chicago Booth School of Business.
A Simple Model – Free LBO Modeling Tutorials
Arguably the best free LBO tutorial series, with unedited walkthroughs and downloadable Excel files. Highly practical for learning LBO modeling from scratch.
OpenBB – Open-Source Financial Data Platform
The most credible open-source Bloomberg alternative, providing financial data and analytics for equities, fixed income, and macroeconomic data.
numpy-financial – Financial Functions for Python
Free Python library covering basic financial functions: NPV, IRR, PMT, and amortization — essential building blocks for financial modeling.
AbsBox – Open-Source ABS/MBS Cashflow Modeling Library
Remarkable open-source Python library specifically designed for ABS/MBS cashflow modeling, with human-readable waterfall definitions and sensitivity analysis capabilities.
Chandoo.org: Master Excel for Financial Applications
A highly respected website offering extensive free tutorials, tips, and articles on advanced Excel techniques, charting, data analysis, and VBA, crucial for building robust financial models and dashboards.