NotePlan is described as 'With NotePlan you get serious work done. It helps you to capture important details and keep track of things at work. Manage your calendar, todos and notes in one place. Find out how! HERE’S HOW IT WORKS 1. Capture Your Thoughts' and is an app in the Office & Productivity category. There are more than 25 alternatives to NotePlan for a variety of platforms, including Windows, Mac, Online / Web-based, iPhone and Android. The best alternative is Joplin, which is both free and Open Source. Other great apps like NotePlan are Obsidian (Free Personal), Evernote (Freemium), Zim (Free, Open Source) and Zettlr (Free, Open Source).
Joplin is a free, open source note taking and to-do application, which can handle a large number of notes organised into notebooks. The notes are searchable, can be copied, tagged and modified either from the applications directly or from your own text editor.
Zettlr is a supercharged markdown editor that combines many writing editor features and collect them in one application. It aims at speeding up your workflow and help you write without any interruptions.