English Grammar Guide (EGG) is a handy English language reference guide that contains information about:
• Parts of Speech (including the classifications of each as well as their rules)
• Tenses (with explanation and examples)
• Punctuation Rules (with samples)
• Kinds of Sentences (according to form and use)
• Subject and Predicate (how they differ)
• Modals (includes examples and explanation on how to use them)
• Affixes (includes kinds of affixes and samples)

This is a useful English app for English teachers, students, ESL learners and even ordinary people who want to make sure their grammar is okay. :-)