I last wrote about digital comic reader software back in 2015, which in technology and digital media terms is quite awhile ago. Thus, an update's long overdue.
Digital comics are still popular, even if they make up a slim portion of overall comic book and graphic novel sales. Services like Comixology, Marvel Unlimited, and DC Universe are popular subscription services for digital comic reading. However, there's still a need for stand-alone comic reader apps, such as for reading comics bought from Humble Bundle.
The apps listed below support the most popular comic file formats (such as CBR, CBZ, and PDF). If you're looking for digital comic services like Comixology or Marvel Unlimited, see my previous post on how to start reading digital comics. All of the apps I list are free, though some offer premium versions/features.
Android: Perfect Viewer
While I switched from Android to iOS some time ago, I preferred Perfect Viewer as my Android comic reader of choice. It's one of the older and better readers for Android, and works well. The only caveat is the controls might have a slight learning curve, as the app was originally geared toward manga.
On my iPad, I've found Panels as my iOS app of choice. The interface is clean and easy to use, and it makes reading comics enjoyable. Files can also be accessed from cloud services (Dropbox, iCloud, etc.).
Desktop / laptop computers
Windows, Linux: MComix
MComix is my choice of comic reader on Linux installations; fortunately, it also has a Windows version. The reader comes with various features, and works pretty well.
The only issue with the Windows version is there's no installer to install it (and appear alongside the other apps in the Start menu); it's ready to launch by double clicking the app itself, however. I opted to just keep the MComix folder/app under my own user directory, but pinned the app to the bottom menu bar. I also reassigned CBR/CBZ format files to open with MComix.
MacOS: Simple Comic
Simple Comic is my choice of comic reader on Macs. Similar to Panels above, it's easy to use and works well. Per its name, it has a very simplified and streamlined interface.
The only concern might be it's a bit older at this point (it doesn't seem to have been updated in awhile). Though a brief check suggests it still works on modern Macs.
I never really found a good comic reader for my Chromebook. One reason is that Chrome OS' handling of ZIP/RAR files in my experience has been lackluster. (CBR and CBZ files are just renamed ZIP/RAR files.)
However, Chrome OS now has support for both Android and Linux apps built-in. The latter requires going into the settings to turn on Linux support. Thus, the Android and Windows apps I suggested above should run fine on Chromebooks.