There is a handful of apps that seem to be official, allowing people to read manga for free or a small fee. But many of these apps aren’t really legal. While not hosting the manga themselves (making them harder to get shut down) many of them point to fan scanned and sometimes fan translated versions of manga. This doesn’t support the works and don’t help your favorite manga get more releases or an anime release. Of course you could always buy the manga in it’s printed edition, which likely show the most support. But with all the Video Streaming sites we have very few manga streaming as of now.
The Subtitle streaming site also has a manga area. While not a very strong manga section but if you already have a Crunchy Roll subscription then it’s included. Crunchyroll video library for state side is one of the biggest although only if you enjoy subtitle anime. With about 50ish mangas in the library at time of writing this, they have some popular stuff. Attack on Titan, Seven deadly sins, Raising of the Shield Hero, even some newer things like the creator of Fairy Tail’s new works Edens Zero. You can find the selection here.
Now own by Amazon Comixology isn’t hiding the focus of the focus on comics. They do now have a Manga area. They sell digital manga as well as having a unlimited service some of the Comics and Manga can be seen on. In the Manga area it appears they ether allow some Japan Inspire Comics in to the section or they get some obscure Mangas I never herd of, Although nether is a bad thing to say. While you see some of the same books in Crunchyroll such as Attack on titan and others, we also have things like A Silent Voice, Parasite, and School Rumble in the unlimited read area. You can find the Manga in Unlimited Area here, and the Manga area here.