Any Android app suggestion to read free manga ?
mangadex.org
There's an app called mihon. You can literally download any source and read it.
Extensions ?
tachiyomi
edit: holy moly Mihon is just Tachiyomi but still in development I'm saved, use Mihon Tachiyomi is a good option if you have an older phone
Not an app but Manga4life or mangasee
Nice try Shonenjump employee
mihon
Manga4life for really good quality scans
installed mangazone 4 years ago, never changed it
kotatsu, most polished of the open source reader forks imo
oniyomi with dependancies, can pretty much any website you would normally use