Mihon - Free and open source manga reader for Android
Houdoku - Manga reader and library manager for the desktop
Aniyomi - Aniyomi is an unofficial fork of the free and open source manga reader Tachiyomi that adds anime capabilities!
Suwayomi-Server - A rewrite of Tachiyomi for the Desktop
TachiyomiSY - Tachiyomi is a free and open source manga reader for Android 6.0 and above, based off TachiyomiAZ.
NeeView - Display two images simultaneously