Google Keep is a note taking application developed by Google.
Google Keep is also available as a mobile app for the Android and iOS mobile operating systems and as a web application.
Easy to use for note taking or for making check lists, it's a useful tool which can be used for making that quick mental note about something you don't want to forget, or for creating your daily To Do list. You can set reminders for specific times, and you can even "share" your individual notes with someone else so they can see what needs to be done!
If you haven't used it before I would highly recommend this app.