On my Android devices I use Aldiko and Moon Reader Pro, depending on my mood. On Windows, however, I am still stuck with FBReader and the reader bundled with Calibre, and I don't like very much both of them. (Adobe Digital Edition is a heavy program). I would prefer a standalone program which runs on Windows 7 too, and I don't like browser extension since my browsers already use a lot of RAM. Any suggestions?
You can try IceCream Ebook Reader:
Meet Icecream Ebook Reader, one of the best free EPUB readers that transforms your computer screen into a convenient top-notch ebook reader. The tool enables you read ebooks in EPUB, MOBI, FB2, PDF and other popular formats. Manage your digital library on your PC or Windows-based laptop. This program also features the ability to turn pages, use bookmarks, search your library, track reading progress and much more.
You could try Sumatra PDF; despite the name, this program can read various document formats, including ebooks (
.mobi) and comic books (
.cbr). It's free and open source, and its main features are being a lightweight and portable program; I've tried it a couple of times, and I found it a bit too minimalistic (maybe this is a plus for you), but if you need a program that won't drain your system resources you should definitely give it a try.
Besides that, and not counting other obvious alternatives like Kindle and Kobo readers for PC, I don't have many other suggestions; I'm mainly a Linux user, and I'm fine with Calibre internal reader, so I've never really bothered to look for other things.
You could try to look for something else on alternativeto.net (here and here), but honestly, there seems to be very few ebook readers for PC, if compared with their portable devices counterparts: people mostly like to read ebooks on ereaders or tablets, so I think that developers have less incentive to work on software that runs on a PC.
If you like good support of ePub3 and it’s advantages, give a chance to Azardi Reader or to Readium.
Well built reader with nice support of modern e-books’ features.
Supporting latest standards as far as possible. It is possible to install it in a form of Chrome plugin (or Vivaldi plugin).
The rest, like ADE, are, according to my experiences, a bit unstable. There are plenty of plugins to Firefox as well as Chromium but none of them has as good options and ePub support as these two.
I use them daily for testing. Anyway, these two are those recommended to readers of the publishing house I work for.
You may want to try ePub File Reader.
EPUB File Reader is a free EPUB files viewer, can help you to open and read ePub e-books and documents. The software interface consists of two parts, the left will show document chapter directory, the right is a browser to show document content. This software is easy to use very much, it is a freeware and completely free to use.
If you use Windows 8 or 10, Nook is a really good choice.
Customize your reading experience to view books with different fonts, line spacing and themes, turn pages with the flick of a finger or jump to any page. The app even comes loaded with free book samples. And so you never lose your place, the NOOK app syncs the last page you've read across your tablet and PC.
As someone else said, Ice Cream is pretty good too, if you are on Windows Vista and above.