KOReader is described as 'An ebook reader application supporting PDF, DjVu, EPUB, FB2 and many more formats, running on Kindle, Kobo, PocketBook, Linux and Android devices' and is a popular PDF Reader in the news & books category. There are more than 50 alternatives to KOReader for a variety of platforms, including Android, Windows, Mac, Linux and Android Tablet apps. The best KOReader alternative is calibre, which is both free and Open Source. Other great apps like KOReader are SumatraPDF, Okular, Readest and Librera Reader.