numpy-financial – Financial Functions for Python
by NumPy / SciPy Community
Free Python library covering basic financial functions: NPV, IRR, PMT, and amortization — essential building blocks for financial modeling.
More resources on Excel for Finance
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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
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QuantLib – Open-Source Quantitative Finance Library
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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.