Open source means code is open — it can be freely viewed, modified, and distributed. 96% of internet infrastructure runs on open source applications. Linux, Apache, MySQL, PHP — the LAMP stack created web hosting history. Android, Chromium, VS Code, React, Vue — all are open source.
Open source business models: support and services (Red Hat, Canonical), Open core (core open, extended version paid — GitLab, Elasticsearch), SaaS (MongoDB Atlas), dual licensing. Contributing to open source on GitHub is an excellent portfolio boost. Apache, MIT, GPL, LGPL — different licenses with different restrictions. Copyleft (GPL): if you use open-source code, you must open-source yours too.
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