I supposed that I ought to mention, that I am doing this on a Linux Mint 13 (LTS) MATE PC. I'm not sure if that will make a difference, but there is a possibility that if you're using something else, your experience will differ. Certainly your file manager might not be Caja, but most of the file managers allow you to do the same things.
As stated on the setup page, you can download (this opens in a new browser window) this is the text file that IS droopy. Just right click and save the file as droopy. I opened up Caja as root, as I knew I was going to need root access to change the file permissions, and to make it executable. I copied the droopy file to the /bin dir, and changed the permissions, and checked the box to make it executable. I did made the mistake of giving the file a .py extension, but it doesn't seem to need that.
You might also want to use an avatar.png file like the ones below, as the setup page suggests. It's up to you of course.
$ droopy -m "Hey, it's randy. You can send me a file." -p ~/avatar.png
I was able to click on the http://localhost:8000 in my terminal, to bring up the web page as others should see it, and there's a handy bar at the top of the page that you can click on to get your web page address. That's the address that you want to share with others to get to your computer.
Mind you, you have to make sure that your router allows this. For this, you'll have to know your router's settings and how to allow others past your firewall. If it's just going to be a one time deal, I suppose one could take the risk, and pull their whole firewall down, but I'd not recommend it.
If all goes well, and you don't have a friend to try this out on, you can always do what I did, and test it out with your phone. :)
In any case, I had some fun testing this out, and learning a few things. I hope this can be of some use to someone, and leave a comment if you're so inclined, or a note to me over on G+