GCC Explorer is an interactive compiler. The left-hand pane shows editable C/C++ code. The right, the assembly output of having compiled the code with a given compiler and settings.
Try out the demo site!
GCC Explorer is written in node. Most of the heavy lifting is actually done on the client, which is arguably a bad decision.
Assuming you have npm and node installed, simply running
make ought to get you up and running with a GCC explorer running on port 10240 on your local machine: http://localhost:10240
If you want to point it at your own GCC or similar binaries, either edit the
etc/config/gcc-explorer.defaults.properties or else make a new one with the name