Evernote - Bring your life's work together in one digital workspace. Evernote is the place to collect inspirational ideas, write meaningful words, and move your important projects forward.

TexitEasy - TexitEasy is a free, cross-platform and open-source latex editor.

Standard Notes - A safe place for your notes, thoughts, and life's work

Lagrida Latexeditor - Lagrida Latexeditor is an all-in-one website that lets you edit, write or check the authentication of your mathematical equations or symbols in a decent manner without any hassle.

Joplin - 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, tagged and modified either from the applications directly or from your own text editor.

Hostmath - Hostmath is a user-friendly mathematical symbol or equation editor that provides you an opportunity to edit your entire difficult equation in seconds.