The "Anagram game" is a game of anagrams. The length of each word is 5 letters. All the words in the same category have the same letters. Thus of the same letters, you can make a few words.
In the game, the user will be given a set of letters. He must collect them from the word. Try to find a few words to one set of letters.

Example of anagram: word QUITE has anagram QUIET or the word SMALL has anagram MALLS. Those are two different words with the same letters.
You can generate the anagrams by special sites, for example this anagram generator.

Tip: want to find niche for your app? Try making app for your social group/language. If you know several languages, use less popular one. Targeting small groups of people cam make your app a lot more popular. You'll be able to find niches that are free from huge players on app market and make a great app for your social group.