Hartmut GoebelNomacs ImageLounge (open source, multi platform), is a perfect replacement for irfanview (Windows only): Easy image manipulation, batch processing, slideshows.
Anyhow it is not as well know and as widespread as it deserves.
Can you help completing the translation for your nativ language? Or spread this in your language's community?
If you are a developer and looking for an interesting project: Nomacs is looking for support.