In scope is anything of note in technology/programming that is Danish, Estonian, Finnish, Icelandic, Norwegian or Swedish. I've included the main authors based on Wikipedia articles.
A lot of these were created by people while abroad (mainly in the US) but I still list them here as it's interesting to see how much people from such a small part of the world have contributed. Similarly, things built in the Nordic countries by a multitude of nationalities may be included (e.g. Erlang).
- 1960 - ALGOL 60 "Report on the Algorithmic Language ALGOL 60". Peter Naur (Denmark)
- 1965 - SIMULA. Ole-Johan Dahl & Kristen Nygaard (Norway) https://en.wikipedia.org/wiki/Simula
- 1967 - First Object Oriented Programming language (SIMULA 67). Ole-Johan Dahl & Kristen Nygaard (Norway) https://en.wikipedia.org/wiki/Object-oriented_programming#History
- 1983 - Turbo Pascal. Anders Hejlsberg (Denmark) https://en.wikipedia.org/wiki/Turbo_Pascal
- 1985 - C++. Bjarne Stroustrup (Denmark) https://en.wikipedia.org/wiki/C%2B%2B
- 1986 - Erlang. Joe Armstrong (UK), Robert Virding (Sweden) & Mike Williams (UK). See also Ericsson. https://en.wikipedia.org/wiki/Erlang_(programming_language)
- 1991 - Linux. Linus Torvalds (Finland) https://en.wikipedia.org/wiki/Linux_kernel
- 1995 - PHP. Rasmus Lerdorf (Denmark) https://en.wikipedia.org/wiki/PHP
- 1995 - MySQL. Michael Widenius (Finland), David Axmark (Sweden) https://en.wikipedia.org/wiki/MySQL
- 1995 - InnoDB. Heikki Tuuri (Finland) https://en.wikipedia.org/wiki/Innobase
- 1995 - Opera. See also Telenor. (Norway) https://en.wikipedia.org/wiki/Opera_(web_browser) https://en.wikipedia.org/wiki/History_of_the_Opera_web_browser
- 2000 - C#. Anders Hejlsberg (Denmark) https://en.wikipedia.org/wiki/Anders_Hejlsberg
- 2001 - Kazaa. Jaan Tallinn (Estonia) Niklas Zennström (Sweden) & Janus Friis (Denmark) https://en.wikipedia.org/wiki/Kazaa
- 2003 - Google Maps. Jens Eilstrup Rasmussen & Lars Eilstrup Rasmussen (Denmark) https://en.wikipedia.org/wiki/Google_Maps
- 2003 - Skype. Niklas Zennström (Sweden) & Janus Friis (Denmark), plus Estonians Priit Kasesalu, Jaan Tallinn & Ahti Heinla https://en.wikipedia.org/wiki/Skype
- 2005 - Ruby on Rails. David Heinemeier Hansson (Denmark) https://en.wikipedia.org/wiki/Ruby_on_Rails
- 2005 - μTorrent. Ludvig Strigeus (Sweden) https://en.wikipedia.org/wiki/ΜTorrent
- 2006 - Varnish cache. Poul-Henning Kamp (Denmark) https://en.wikipedia.org/wiki/Varnish_(software)
- 2006 - Spotify. Daniel Ek (Sweden) https://en.wikipedia.org/wiki/Spotify
- 2008 - Chrome V8 JavaScript engine. Lars Bak (Denmark) https://en.wikipedia.org/wiki/Chrome_V8
- 2009 - Minecraft. Markus Persson & Jens Bergensten (Sweden) https://en.wikipedia.org/wiki/Minecraft
- 2009 - Akka. Jonas Bonér (Sweden) https://en.wikipedia.org/wiki/Akka_(toolkit)
- 2011 - Dart. Lars Bak & Kasper Lund (Denmark) https://en.wikipedia.org/wiki/Dart_(programming_language)
- 2012 - TypeScript. Anders Hejlsberg (Denmark)
- 1855 - Telenor (Norway) https://en.wikipedia.org/wiki/Telenor
- 1865 - Nokia (Finland) https://en.wikipedia.org/wiki/Nokia
- 1876 - Ericsson (Sweden) https://en.wikipedia.org/wiki/Ericsson
- 1988 - F-Secure (Finland) https://en.wikipedia.org/wiki/F-Secure