Stackrover 4+

Stackrover is a unique interactive manual, training app, and knowledge base for all JavaScript developers. Build your skills and gain insight while waiting for a lunch or during any dull moment. Ditch all your fears and achieve real mastery step by step. Get prepared for any task you are up to.
Let Javascript finally make sense!
No sign-up, no ads, no recurring fees. Works fully offline.

Key features:

• over 1700 JavaScript-related concepts, constructs, and API elements explained
• detailed yet straightforward descriptions, annotated code samples
• answers to hard questions, tips, warnings, reassurances, lists, and overviews
• Mission board for information related to your current work
• Cheatboard for information you are looking up frequently
• Study board for topics you want to study systematically
• personal notes inserted right into the content
• dynamically generated quizzes
• custom quizzes based on the topics present in your boards

Convenient details:

• memory aids for things that are notoriously hard to remember
• content fine-tuned for high-distraction environments
• Term browser for more curious investigations into topics of interest
• add topics to your Study board directly from a quiz
• links to other useful resources
• instant anonymous feedback to make Stackrover's content ever more useful
• user manual included