What are some great not-so-popular apps?

What are some great apps and games that you’ve found that are very useful and/or fun but nobody seems to know about them?

I think blogger app is pretty good but not so popular.

LectureNotes is so much better than that S Note app Samsung puts on the notes. But it might be quite popular I am not sure. Anyway, if you have a Note, check it out. I have written hundreds of pages on my Note10.1 using it.

May be the developer have not advertised greatly on his app

Papyrus is another great one for the Note.