The first spaced-repetition powered note-taking tool that lets you structure knowledge exactly in the way you think about it.
Write, plan, collaborate, and get organized — all in one tool. Write connected notes with rich format and Export to markdown, pdf, etc.
Taskade is a beautiful project management tool for both personal use and team collaborations. Taskade ships with task management and note-taking tools.
Anydo comes with a very useful daily review and reminder. Anydo also integrates with its own utilities such as calenders.
Not so lightweight but still very good for managing life especially since it has got a lot of integrations from a lot of other services.
Google Keep is light-weight. It comes with powerful search. The App ships with simple drawing and handwriting.