There are many alternatives to wikidPad for Linux and since it's discontinued a lot of people are looking for a replacement. The best Linux alternative is Joplin, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 100 alternatives to wikidPad and loads of them are available for Linux so hopefully you can find a suitable replacement. Other interesting Linux alternatives to wikidPad are Standard Notes (Freemium, Open Source), Google Keep (Free), Obsidian (Free Personal) 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.
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.