The following list contains links with information about WordPress Plugin development. There are official WordPress documentation pages, as well as many other handpicked tutorials, tools and reference pages, in no parrticular order. Have fun!
WordPress Codex – Writing a Plugin
https://codex.wordpress.org/Writing_a_Plugin
WordPress Codex – Plugin Resources
https://codex.wordpress.org/Plugin_Resources
WordPress Codex – Plugin API
https://codex.wordpress.org/Plugin_API
WordPress Codex – User:Skippy
http://codex.wordpress.org/User:Skippy
WordPress Developers Resources – Plugin Handbook
https://developer.wordpress.org/plugins/
WordPress Code Reference
https://developer.wordpress.org/reference/
WordPress Hooks Database by Adam R. Brown
http://adambrown.info/p/wp_hooks
Devin Vinson / WordPress-Plugin-Boilerplate
https://github.com/DevinVinson/WordPress-Plugin-Boilerplate
Getting Started with WordPress Plugin Development: The Ultimate Guide
http://premium.wpmudev.org/blog/wordpress-plugin-development-guide/
A Quick (and in-Depth) Guide to WordPress Hooks
http://premium.wpmudev.org/blog/wordpress-hooks/
WordPress Essentials: How to Create a WordPress Plugin
http://www.smashingmagazine.com/2011/09/30/how-to-create-a-wordpress-plugin/
WordPress Essentials: The Definitive Guide To WordPress Hooks
http://www.smashingmagazine.com/2011/10/07/definitive-guide-wordpress-hooks/
Beginner’s Guide to WordPress Plugin Development
http://www.hongkiat.com/blog/beginners-guide-to-wordpress-plugin-development/
Create a Custom WordPress Plugin from Scratch
http://code.tutsplus.com/tutorials/create-a-custom-wordpress-plugin-from-scratch–net-2668
How to Create a WordPress Plugin
http://www.elegantthemes.com/blog/tips-tricks/how-to-create-a-wordpress-plugin
WordPress Plugin Tutorial: Developing a Plugin from Scratch
https://www.airpair.com/wordpress/posts/developing-wordpress-plugin-from-scratch
List all hooked WordPress functions
http://www.wprecipes.com/list-all-hooked-wordpress-functions
WordPress Coding Standards
https://make.wordpress.org/core/handbook/coding-standards/
Inline Documentation Standards
https://make.wordpress.org/core/handbook/inline-documentation-standards/
Developing a WordPress Theme from Scratch by Tania Rascia
https://www.taniarascia.com/developing-a-wordpress-theme-from-scratch/
Roots | Modern WordPress Development Tools
https://roots.io/
Underscores – A Starter Theme for WordPress
https://underscores.me/
GenerateWp
https://generatewp.com/
How to Create a WordPress Plugin
http://www.wpbeginner.com/wp-tutorials/how-to-create-a-wordpress-plugin/
Learning How to Create a WordPress Plugin the Right Way
http://chrislema.com/create-a-wordpress-plugin/