Evernote
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.
Free plan
WebMac
Agenda
Agenda is a note-taking app that ties notes to a calendar, reminders and projects.
What it does
- Built-in calendar and reminders
- Full-fleged editor
Similar tools
Google Keep
Google Keep is light-weight. It comes with powerful search. The App ships with simple drawing and handwriting.
Free
WebAndroid
Taskade
Taskade is a beautiful project management tool for both personal use and team collaborations. Taskade ships with task management and note-taking tools.
Free plan
WebMac