Tools for thought – ways to organise and develop thinking.
Has been around for ages. People used to use index cards where they wrote down pieces of information or research they were working on.
Index cards are by nature non-linear, but could be arranged in a linear way to create a manuscript for a book.
Now sometimes referring to note-taking tools with bidirectional linking abilites.
New software that structure your notes as a graph are very helpful for exploring your knowledge in new ways.