Ideas of connected ideas
Commonplace book, Memex, Hypertext, Hypercard, Zettelkasten, Wiki, … all share the same idea: we want to have a central place to store ideas (External brain) that are organically connected together, just like they are represented in our mind. The ability to make associations is critical for making information discoverable and nudging new thoughts (combinations of ideas).
For instance, Niklas Luhmann is well-known for attributing his productivity and the breadth of knowledge to his extensive use of the Zettelkasten method.
What are the tools for creating such a system? Probably the simplest digital system is just a folder with a bunch of Markdown files. Obsidian is a great tool that can manage such a system. It’s built on Markdown flat files that are connected through Wikilinks. It provides powerful features such as searching, backlink-updating, and many plug-ins, leveraging the strength as an offline software (you can pay to get it published as well).
Of course, one can use a slip box (Zettelkasten) and analog solutions have their own benefits and charms, but it is hard to deny that they are quite limited compared with digital tools. Many people used to use a personal Wiki to access the information via the web interface. There were many wiki solutions, but it seems like they are slowly converging into Markdown (See The Rule of Least Power).
There are commercial tools too. Roam research, notion, etc. are all emerging as a nice twist to the classic Wiki. I don’t really use them because they are not as good as obsidian in core functionalities while being somewhat bloated. Probably the most crucial factor is that the data is tied to their service, not flat files that I can manage as I see fit.
I came across Obsidian while trying to build my own wiki solution that’s built on flat markdown files and Git. I ended up building the wiki app that simply uses a repository of markdown files that can be also used by Obsidian. The data is in a Github repo and both YYiki and Obsidian reads from and writes to the repo. If you want to have the capability to use your second brain as a wiki, you can check out the YYiki.