Elder Futhark evolved into Younger Futhark, with the transition happening between 650 AD and 800 AD. Younger Futhark was most different from Elder Futhark in the number of characters: Younger Futhark had only two-thirds as many letters as Elder Futhark. You might think that this was because the language simplified, and there weren’t as many sounds in Norse during the Younger Futhark period. You might be wrong, however. Linguists believe that the number of sounds in the spoken language actually increased over the transition period.
Archeologists also believe that literacy significantly increased during this period. Maybe the new learners were lazy; maybe as time went on, people discovered that you could still read things even without as many characters as the language needed. I don’t know.
One common use of this writing system was to keep track of the Christian calendar, which uses the 19-year Metonic cycle of “golden years”. They used one Younger Futhark character for each of the years, which meant that they were three characters short. To handle that, they invented three characters which were only used to represent those three years’ numbers.
Futhark was written in all kinds of ways. In addition to left-to-right, right-to-left, and boustrophedon, the writing also frequently followed the outlines of the object that it was inscribed upon.
Younger Futhark had two styles: the long-branch (or Danish) and short-twig (or Swedish/Norwegian) versions. Like the names suggest, the short-twig version had shorter and/or more abbreviated strokes.
A variant, used in a area of Sweden between the 10th and 12th century, called Hälsinge Runes took this to extremes. In these runes, the vertical bar was completely removed from most glyphs, leaving very short lines to represent the runes. It might be that Hälsinge Runes were the very first shorthand.