TeX Live is a widely used TeX distribution. It is published annually, and is available by both download and on DVD.
If you’d like a free copy of TeX Live, and live in the UK, please email uktug-committee@uk-tug-archive.tug.org.
Visit http://tug.org/texlive/ for more information about TeX Live.
If you plan to install TeX Live on a Raspberry Pi then there are some special considerations; look here: http://uk-tug-archive.tug.org/texlive/texlive-on-raspberry-pi/.