sumatrapdfreader/sumatrapdf

OBS Studio (obsproject/obs-studio) is a free video capture and streaming tool released under GPL-2.0. Its topics list points to game capture, screen capture, DirectShow device input, and streaming built around Twitch, YouTube Live, and Facebook Live, and the project funds itself through Patreon, OpenCollective, and PayPal.

MarkItDown is Microsoft's open-source Python library for converting PDF, Office, image, audio, and web files into Markdown, aimed at LLM and RAG pipelines rather than human-facing formatting. It ships as a CLI and a Python API, with optional Azure Document Intelligence and Content Understanding backends for cloud-based extraction of scanned documents and structured fields.

Bitcoin Core is the reference implementation of the Bitcoin protocol, hosted at bitcoin/bitcoin on GitHub. Per its README, it joins the Bitcoin peer-to-peer network to independently validate blocks and transactions, ships an optional wallet and GUI, and is written in C++ under the MIT license.

Public APIs is a community-curated GitHub repository listing free, publicly accessible APIs across a wide range of categories, with auth type, HTTPS, and CORS noted for each entry. It's a browsable reference, not a library to install.