"Run Command" for Atom
Execute any arbitrary command in Atom. Originally derived from Phil Nash's Ruby Quick Test.
Usage
ctrl-r to open up this:

Enter a command, enter to run it:

ctrl-r, enter, and run it again:

Put it all together, and you can do this:

(You can also toggle the command output with cmd-ctrl-x, or kill the last command with cmd-ctrl-alt-x)