I've been wanting to start reading more English-translated digital manga on my Kindle Fire HD, but I like books published by many different companies, and I'd like to keep any potential digital manga collection I create tied to as few different app sources as I can.
My questions is: is there any digital manga app that currently collects all digitally-published manga? If not, what are some apps that, while not having all series, do offer titles from different publishers, and how extensive is their selection?
As per Hakase's comment, info on sources for legal DRM-free English manga would also be appreciated. Ignore if this makes the question too broad.