MyNotex is described as 'free software for Gnu/Linux useful to take and to manage textual notes, also a large number of them. Notes are gathered under different subjects and are made by a title, a date, a tags (keywords) list and a free-length text' and is an app in the Office & Productivity category. There are more than 50 alternatives to MyNotex for a variety of platforms, including Windows, Android, Mac, Online / Web-based and iPhone. The best alternative is Joplin, which is both free and Open Source. Other great apps like MyNotex are Standard Notes (Freemium, Open Source), Microsoft OneNote (Freemium), Evernote (Freemium) and Simplenote (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.