Copied from the FAQs on the IrfanView website:
Q: Can I use IrfanView on Mac?
A: Yes, probably. There is no native-Mac version of IrfanView. However, you can use IrfanView in conjunction with Mac program like WineBottler/DARWINE. Take the ZIP version of IrfanView and unzip it or copy your existing Windows IrfanView folder to Mac. This is easier because the installer may need additional Windows DLLs to run.