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 gcc-explorer.YOURHOSTNAME.properties. The config system leaves a lot to be desired, I'm working on porting CCS to javascript and then something more rational can be used.
Feel free to raise an issue on github or email me directly for more help.