1) https://longform.org/ http://itunes.apple.com/us/app/longform/id490437064?mt=8
2) https://usepanda.com/ https://itunes.apple.com/us/app/panda-lite/id934805959?mt=8
3) https://redef.com/ app not in appstore
4) medium
5) feedly
Longform has a particularly attractive feature that restores your spot in a page when iOS terminates the app. Longform and Panda and Redef are all incredibly useful without customizing them.
If you are looking for sources check out Panda AND these lists https://redef.com/charts/sources/total http://www.aldaily.com/media http://scitechdaily.com/resources/ http://www.techmeme.com/lb http://www.mediagazer.com/lb http://www.memeorandum.com/lb https://longform.org/archive/publications https://longform.org/archive/writers
I prefer when "save for later" buttons are customizable, so you can set it to save to pocket, pinboard, feedly etc.