What applications can be used for viewing .exr files?

I tried installing gwenview but doesn't seem to work for me.

Can anyone recommend their favorite application for viewing .exr, .png files and sequences?

Only viewer per se that I know of working for exr files out of the box is exrdisplay, which is part of the package openexr-viewers (you can install it with sudo apt install openexr-viewers). Can't imagine why they put an "s" at the end of the name. Looks like just one viewer to me. If Gwenview can be made to show exr images it is probably through a plugin. It has an import facility under the plugins menu.

More generally, for images I like Viewnior.

The best .exr file viewer for Ubuntu (and windows) is DJV http://djv.sourceforge.net/.
He provides the best experience for file sequences, reviewing, color picker, .exr extra layers display out of the box.

PS: the latest version 1.2.6 on latest Ubuntu gives an error about a missing OpenGL lib! solved with these commands:

sudo apt-get remove --purge libgl1-mesa-dev
sudo apt-get install libgl1-mesa-dev

You can try mrViewer, which can be obtained at sourceforge, too. At:

https://sourceforge.net/projects/mrviewer/files

It handles all types of exr files, including cropped ones, multiview and multipart ones and deep exr files.