Do you have a second brain? 🧠

For anyone unfamiliar: A second brain is the idea of using digital software to help you with remembering everything you want to remember and recall accurately. By offloading the remembering to a searchable digital app, you free your brain up to think. Do any PH-ers make use of a second brain or have another system for managing their learning & knowledge? What do you use and how do you organise it?