What is the best alternative to Atlas・Daily Vocabulary Builder on iPhone?

Vocabulary - Learn words daily, S tier, #1 in daily vocabulary.

Is there a free alternative to Atlas・Daily Vocabulary Builder?

Yes: Vocabulary - Learn words daily (S tier, #1) is free to download, with in-app purchases.

Yes. 2 apps rank above it in daily vocabulary: Vocabulary - Learn words daily (#1), Word of the Day・Vocabulary (#2).

Atlas・Daily Vocabulary Builder is A tier, #3 of 8 in daily vocabulary. Here is everything that competes with it on iPhone, in tier order.

1
Vocabulary - Learn words dailyShigher tier
Free + IAP · ★ 4.8 · 220,615 ratings · score 97
Word of the day app with a widget and games for learning new English words at your own level and pace.
2
Word of the Day・VocabularyShigher tier
Free + IAP · ★ 4.7 · 38,983 ratings · score 95
Free vocabulary app with daily words, 1-minute spaced-repetition quizzes, word games, and themed crosswords.
4
Word of the Day: WidgetA
Free + IAP · ★ 4.2 · 1,622 ratings · score 86
Shows one English word a day on your Home Screen and Lock Screen, with definition, pronunciation, example and audio.
5
LookUp: English Dictionary AppA
Free + IAP · ★ 4.7 · 3,145 ratings · score 83
English dictionary with Oxford definitions, Word of the Day, spaced repetition quizzes and personal word collections.
6
Vocabulary Builder by KnudgeB
Free download · ★ 4.7 · 1,746 ratings · score 78
Vocabulary app that teaches new words through flashcards, word games and spaced repetition in 5-minute daily sessions.
7
Vocab: Learn English WordsB
Free download · ★ 4.7 · 2,129 ratings · score 76
Free English vocabulary app with a daily word, quizzes, word games, flashcards, pronunciation audio, and offline mode.
8
Learn Spanish with Easy TenD
Free + IAP · ★ 4.6 · 3,000 ratings · score 50
Free app for learning foreign languages by adding 10 new words a day, with voiced words and a 5-minute daily routine.

What is the best alternative to Atlas・Daily Vocabulary Builder on iPhone?: Vocabulary - Learn words daily, S tier, #1 in daily vocabulary.
Is there a free alternative to Atlas・Daily Vocabulary Builder?: Yes: Vocabulary - Learn words daily (S tier, #1) is free to download, with in-app purchases.
Does anything rank above Atlas・Daily Vocabulary Builder?: Yes. 2 apps rank above it in daily vocabulary: Vocabulary - Learn words daily (#1), Word of the Day・Vocabulary (#2).