Doomreader
Vocabulary builder app: learn words from the books you read
A word learned from a list is gone by Friday. A word you met in a story, in a sentence you wanted to finish, has a place to live. Doomreader is a reading app that keeps those words for you: look one up while you read and it is saved with the sentence you found it in, ready to come back to.

It is free on Android, on iPhone through the browser and on any computer, with no sign-up to start. Bring your own books, or start with the easy English classics already inside.
How a word gets saved
Press and hold a word in any book. Beside it come Define, which opens its meaning on Google, and Save word. With the app in another language and an English book, Translate opens Google Translate in your language too. Tap Define or Translate and the word is saved as well: that is the setting Save words I look up, on from the start, and you can turn it off.
Each word is kept once, with the newest sentence you met it in, the book and the day, and a dotted underline marks it in the text so you see it again where it lives. Doomreader keeps no definitions of its own; the meaning is always one tap away. Try it on Winnie-the-Pooh, an easy first book.
Your Words tab
Every word you save is in the Words tab of your Saved page: the word large, the sentence under it with the word in bold, the book and the day. Each has Define and Delete, and Translate when the app is in another language, and a tap opens the book at that very sentence, so a word is never cut off from its story. Saving words and the list are free, in the free classics and in your own EPUBs and PDFs. Save a few from The House at Pooh Corner and the tab fills up fast.
Flashcards every day
With Pro, saved words come back as flashcards in a short daily practice at the top of your Words tab, Words to practise: the word and the sentence where you met it, up to 10 words a day. Tap to check, open Define or Translate if you need to, then mark it I know it now, and it retires, or Keep practising, and it comes back later. A new word first comes up the next day; each Keep practising sends it back after two weeks, then a month, and on out to eight months, so the words you struggle with get the most turns.
Pro also syncs your words across your devices; without it, they stay on the device where you saved them. A chapter of Ozma of Oz a day is plenty to feed it.
Start with a book at your level
The words stick best when the story is easy enough to enjoy. Discover has an Easy English shelf: whole books with short sentences and everyday words, from Winnie-the-Pooh to Alice's Adventures in Wonderland. For short reads with a level on each, see simple English stories for beginners and English reading practice.
For a route, the reading paths go easiest first: the beginner path, the intermediate path and the advanced path, eight whole books each.
Listen while you read
Not sure how a word sounds? Tap the headphones and your device's own voice reads the book aloud from the post on screen, highlighting the sentence as it goes, free. Slow it to 0.75x for a hard chapter. Try it on A Christmas Carol, or see free audiobooks.
What it is not
Doomreader is not a course and not a word-of-the-day app. It has no built-in dictionary, no quizzes on words you never met and no lists to memorise. It is for learning the words of what you actually read, one sentence at a time. If you want drills and grammar lessons, use a course beside it; if you want to read more and keep what you learn, this is built for that: start with English Fairy Tales, short tales in plain English.