WordPress plugin which displays responsive stage based on browser width:
>= 960px
768px - 959px
480px - 767px
<= 479px
This helps in building CSS media queries, as you can quickly see what stage you are in when resizing your browser.
Options include ability to switch which corner the flag is displayed in, colors (so as to be distinguishable
from your design), as well as whether to show only to admin or not.