I downloaded an Epson printer driver the other day. It was a HQX file. HQX is an old mac format used for file transfers. It's called "hex" for some reason. I don't remember of it is compressed or just provides some sort of protection against corruption on mixed networks. It's antique.
I opened the HQX file and found a SEA file. SEA stands for Self-Extracting Archive. It's a file format that provides both compression and an application to decompress. Wow, you don't see many of those anymore. Also antique, but apparently still kicking as it was an OS X application.
Inside the SEA, there was a folder and inside the folder was a DMG. A DMG is a disk image. These are very popular now and are the usual way that something like a printer driver would be distributed. DMG is a compressed format. I wonder why they felt like they had to compress a compressed format. Normally a DMG is the final layer, but no . . .
I mounted the DMG and within there was an install program, a Vise installer. As far as I know, the Vise installer also provides compression. This vintage of installing software is somewhat older than the DMG and somewhat newer than HQX. So they compressed a compresssed, compressed file, put two applications in there and added a funny format as the very top layer.
Fortunately, when I double-clicked the installer, my drivers actually installed. I can only imagine that they were much smaller than the file I downloaded from Epson, who has a rather slow server. The drivers are fine, but the release engineer is an idiot. This process took more than half an hour.