I like SimplyRain. It makes the silence of my room less deafening.
Some apps I use are:
Texter, a text substitution app.
Anki, a flashcard and spaced-repetition app that helps me stop forgetting what I have learned.
Memorization Tool, which creates first-letter cues for a piece of text that you may want to memorise. For example:
In Xanadu did Kubla Khan
A stately pleasure-dome decree:
Where Alph, the sacred river, ran
Through caverns measureless to man
Down to a sunless sea.
So twice five miles of fertile ground
With walls and towers were girdled round;
And there were gardens bright with sinuous rills,
Where blossomed many an incense-bearing tree;
And here were forests ancient as the hills,
Enfolding sunny spots of greenery.
Becomes:
I X d K K
A s p-d d:
W A, t s r, r
T c m t m
D t a s s.
S t f m o f g
W w a t w g r;
A t w g b w s r,
W b m a i-b t;
A h w f a a t h,
E s s o g.