TinyELF

This is a binary file you can use to make really small Linux/ELF executables for x86-64:

$ ./helloworld              # a tinyelf
hello world
$ ./helloworld-c            # compiled with gcc
hello world
$ wc -c helloworld-c helloworld | grep -v total
1733 helloworld-c
 333 helloworld
$

The machine code for helloworld and helloworld-c is identical; each was compiled from helloworld.c.

Using TinyELF

$ gcc helloworld.c -nostdlib -o helloworld-c
$ objcopy -O binary -j .text helloworld-c helloworld-bin
$ cat tinyelf helloworld-bin > helloworld
$ chmod +x helloworld

You then have a tiny executable that you can run normally:

$ ./helloworld
hello world!
$

See helloworld.c for some important caveats and things you need to do in order for this to work. In particular, some of the obvious limitations are that you can't use libc or have any global data, including string literals.