Portar MSX tech doc: http://problemkaputt.de/portar.htm

MSX Technical Data Book: http://www.tabalabs.com.br/msx/msx_tech_hb/msxtech_tabalabs.pdf

MSX2 Technical Handbook: http://www.konamiman.com/msx/msx-e.html#msx2th

The MSX Red Book: https://github.com/oraculo666/The-MSX-Red-Book

Hans Otten MSX Info pages (archive): https://web.archive.org/web/20180726165637/http://msx.hansotten.com/

MSX Assembly page: http://map.grauw.nl/

Although RuMSX is already quite an outdated MSX emulator, it still has best structured and formatted MSX-documentation included that exists. Download, install and open help! http://www.lexlechz.at/en/software.html

For people who read Japanese MSX-Datapack is one of the best resources: http://www.konamito.com/msx-datapack/