This page is intended to provide an overview of the spelling reforms of the Norwegian Nynorsk standard used in education and government. This does not determine what is obsolete or not.
The first official spelling for Nynorsk. At this point, Nynorsk was still called Landsmaal (Landsmål in later spelling). There were two competing standards of Landsmål, but only one of them was made the official one: Hægstadnormalen. The other standard, Midlandsnormalen, could still be used by students. Some features of Midlandsnormalen were eventually incorporated into the official Nynorsk spelling as alternative forms; but by and large, it was Hægstadnormalen that prevailed.
This reform introduced a lot of alternative forms, moving Nynorsk closer to Bokmål. The letter Å also came into official use this year, in both Nynorsk and Bokmål.
This reform continued the trend from 1917 and moved Nynorsk yet closer to Bokmål.
This reform did among other things reduce the status of certain official word forms, making them "second-tier".
This reform was the first that abandoned the idea of a merger with Bokmål. It moved Nynorsk closer to Bokmål in some areas (such as by removing the traditional -i ending for two of the feminine noun classes) and further away in some areas (such as by removing the monophthong forms with -ø- in many words, letting only the diphthong forms with -øy- remain).
A PDF document (in Norwegian) from the Language Council of Norway detailing the changes made is available.
Since the spelling reform of 2012, a plethora of minor revision and decisions has been made.