I did some Googling but frankly there are too many out there, and I am looking for a specific set of functions. Here is my need-have feature list:
Not folder based (or at least not only) - I want to point it to a directory and have it show me thumbnails of each image it can find within this directory, obviously descending and "recursing" into any subdirectories. If it can read archive files containing images, even better :-)
Open-source. I don't want to start a discussion, but in my opinion commercial software often is too rigid or buggy. I don't correlate it to the fact that it is closed source or commercial, but it is my experience - I have no opinion why this is so. Not to say open-source software doesn't often suck at least just as much, but well maintained open-source projects usually fare better than equally well maintained closed-source ones.
Not a MUST, but since I am a desktop user like the most of us, I would like it to be as native an application as possible. I use Ubuntu Linux x86 32-bit. That means GNOME and GTK Please no Java (too slow for my old PC) or KDE. This is also why I avoid closed-source - I haven't seen all that many closed source applications that use GTK.
What are my options here?
I have written this post after I wanted to browse my /usr/share/icons in a convenient matter, as an index, without clicking manually through directories it contains (there are A LOT of these there). That's where I realized I don't have or know the kind of application that'd do this for me.