Things that are free that people don't realise are free

[JohnyBlue]

Different from the tools thread. Not software specifically, just things in general. The services, experiences, or resources that people either do not know are free or assume have a cost attached.

[Marcus]

The entire UK national museum and gallery collection. The British Museum, the National Gallery, the V&A, the Science Museum and many more are free entry. The rest of the world finds this genuinely extraordinary.

[Liam71]

NHS 111 online and by phone. Obvious to UK residents but not obvious to everyone how comprehensive the triage and advice service is before needing a GP appointment.

[BitSus]

Most public libraries still exist and still work. Not just books but audiobooks, ebooks through the Libby app, magazines, free internet access, and in many cases free community events.

[WildManCena23]

Local walking guides produced by councils and National Park authorities. Downloadable as PDFs, often with OS map references, completely free, and frequently better than anything you would buy.

[veritas.io]

The Wayback Machine at archive.org. If you need a version of a web page that no longer exists, it is often there. Also an extraordinary archive of old software, music, and literature.

[CobyOlaleye]

Companies House records for UK registered companies. Full accounts, director histories, filing history, all free and public. Useful for due diligence on any business you are thinking of working with.