Question: What is the license of the EPUB reading software that supports PostScript files if Ghostcript is installed ?

text: EPUB
Software -- Reading software
The following software can read and display EPUB files :
EPUB is an e-book file format that uses the .epub file extension. The term is short for electronic publication and is sometimes styled ePub. EPUB is supported by many e-readers, and compatible software is available for most smartphones, tablets, and computers. EPUB is a technical standard published by the International Digital Publishing Forum (IDPF). It became an official standard of the IDPF in September 2007, superseding the older Open eBook standard. The Book Industry Study Group endorses EPUB 3 as the format of choice for packaging content and has stated that the global book publishing industry should rally around a single standard. The EPUB format is implemented as an archive file consisting of HTML files carrying the content, along with images and other supporting files. EPUB is the most widely supported vendor-independent XML-based (as opposed to PDF) e-book format; that is, it is supported by almost all hardware readers, except for Kindle.
Software License Platform DRM formats supported Notes
Adobe Digital Editions Proprietary Microsoft Windows , Apple Mac OS X Adobe Content Server Requires online activation for ePub files with DRM
Aldiko Proprietary Android Adobe Content Server Supports ePub for Android devices
Apple Books Proprietary OS X , iOS FairPlay Supports EPUB 2 and EPUB 3 . Books not readable directly on computers other than Macs
AZARDI Freeware Windows , OS X , Linux , Android , Apple iOS proprietary ackage obfuscation Supports ePub 3 , ePub 2 . Fixed Layout , SMIL , DRM , MathML , Online and Mobile versions are available when used with AZARDI : Content Fulfilment Server
Bluefire Reader Proprietary Apple iOS , Android Adobe Content Server Supports ePub for Android and iOS devices
calibre GPL Windows , OS X , Linux None Primarily for library management , conversion , and transferring to devices , it includes an EPUB reader and editor . About . Calibre . .mw-parser-output cite.citation { font-style : inherit } .mw-parser-output .citation q { quotes : \\ '' } .mw-parser-output .id-lock-free a , .mw-parser-output .citation .cs1-lock-free a { background : url ( //upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png ) no-repeat ; background-position : right .1em center } .mw-parser-output .id-lock-limited a , .mw-parser-output .id-lock-registration a , .mw-parser-output .citation .cs1-lock-limited a , .mw-parser-output .citation .cs1-lock-registration a { background : url ( //upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png ) no-repeat ; background-position : right .1em center } .mw-parser-output .id-lock-subscription a , .mw-parser-output .citation .cs1-lock-subscription a { background : url ( //upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png ) no-repeat ; background-position : right .1em center } .mw-parser-output .cs1-subscription , .mw-parser-output .cs1-registration { color : # 555 } .mw-parser-output .cs1-subscription span , .mw-parser-output .cs1-registration span { border-bottom:1px dotted ; cursor : help } .mw-parser-output .cs1-ws-icon a { background : url ( //upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Wikisource-logo.svg/12px-Wikisource-logo.svg.png ) no-repeat ; background-position : right .1em center } .mw-parser-output code.cs1-code { color : inherit ; background : inherit ; border : inherit ; padding : inherit } .mw-parser-output .cs1-hidden-error { display : none ; font-size:100% } .mw-parser-output .cs1-visible-error { font-size:100% } .mw-parser-output .cs1-maint { display : none ; color : # 33aa33 ; margin-left:0.3em } .mw-parser-output .cs1-subscription , .mw-parser-output .cs1-registration , .mw-parser-output .cs1-format { font-size:95% } .mw-parser-output .cs1-kern-left , .mw-parser-output .cs1-kern-wl-left { padding-left:0.2em } .mw-parser-output .cs1-kern-right , .mw-parser-output .cs1-kern-wl-right { padding-right:0.2em }
Microsoft Edge Proprietary Windows 10  Microsoft Edge will end support for e-books that use the .epub file extension over the next several months . August 30 , 2019 - KB4512941
EPUBReader Proprietary Mozilla Firefox None Firefox add-on , so runs on any OS that Firefox runs on . EPUBReader home page
FBReader Proprietary Windows , Linux , Android , PDAs , OS X None
Google Play Books Proprietary Web application , Android , Apple iOS Lektz DRM Supports downloading purchased books as ePub and/or PDF
Kitabu Proprietary OS X None Supports ePub3 , ePub2 , Fixed layout
Kobo Proprietary Windows , OS X , Android , Apple iOS , Kobo eReader Software , Adobe Content Server Supports EPUB 2 and EPUB 3
Lektz Readers Proprietary Web application , Google Android , OS X , iOS , Windows Lektz eBook Readers for PDF , ePUB/2 and ePUB3 providing uniform experience across different platforms - iOS , Android , Windows PC , Mac Desktop and Web
Lucifox GPL Windows , OS X , Linux None Ebook reader add-on with annotations for Firefox . Supports open standard ebooks in EPUB 3- and EPUB 2 format and retrieval of books from OPDS book catalogues
Okular GPL Windows , OS X , Linux unknown
Readium BSD All web browsers and all platforms Multiple-DRM implementations Exists as a cross-browser solution for embedding in users websites ( Readium CloudReader ) , a Chrome extension and a cross-platform SDK
Snapplify Proprietary All Web browsers , Apple iOS , Android Adobe Content Server Snapplify SnappSafe DRM Supports downloading purchased books as ePub and/or PDF . Supports PDF , ePUB2 and ePUB3 standard of ebooks
STDU Viewer Freeware Windows  Supports many documents format including ePub
Sumatra PDF GPL Windows Adobe Content Server Supports ePub for devices