My personal go-to mobile application is Youth4work's UPSC 2018.
I would suggest Unacademy as the best educator app. In fact, I personally follow Unacademy to study various topics with the best educators provided by them. Its the best app as in this the educators are those only who have already cleared them. All the educators in the unacademy are very cooperative and every one helps in their best possible manner to clear their student doubts. What I like most about unacademy is they really appreciate student for study. They give daily 10 credits for 10 minutes learning and your credits increases daily and these credits can be used to talk to unacademy educators and also buying plus courses with 10% discount on every plus course.
It's a great app! Give it a try.
1. Mission UPSC - You can get notes (printed/handwritten) of every recognise coaching here, NCERT books, currents affairs books of different coaching, optional notes, Ranker's notes, UPSC relevant books and so many other things which is useful for UPSC.
2. VisionIAS - Video lectures of visionIAS, printed notes, current affairs and other things, model answers of previous year questions.
3. NCERT books
4. PIB - PIB news and ALL INDIA RADIO news
6. Upsc papers
7. Upsc syllabus
Other than this there is a channel of The Hindu zone on TELEGRAM app in which daily all the newspaper (The Hindu, TOI, IE, DAINIK JAGRAN etc) uploaded in pdf version.
You can also subscribe study IQ education channel on YouTube where daily The Hindu editorial brief discussion video upload in Hindi as well as in English.
My personal go-to mobile application is Youth4work's UPSC 2018. The tests, the study material, everything is good. The presentation and design are good and it's easy to understand. I learned a lot from this app.