FatELF is a file format that embeds multiple ELF binaries for different architectures into one file. This is the Linux equivalent of what Mac OS X calls "Universal Binaries."
The format is very simple: it adds some accounting info at the start of the file, and then appends all the ELF binaries after it, adding padding for alignment. The end of the file isn't touched, so you can still do things like self-extracting .zip files for multiple architectures with FatELF.
FatELF lets you pack binaries into one file, seperated by OS ABI, OS ABI version, byte order and word size, and most importantly, CPU architecture.
Work is focused on GNU/Linux, but this could be applied to most modern Unix systems: the BSDs, Solaris, etc.