This is a little late (your students should be busily hacking away/getting ready to upload by now) however, some things to think about for those still struggling
First, look at all the stuff that was done during the year in CSP... all the protocols are actually apps that are out in the real world. Maybe they can make/simulate them.
Also, there are lots of books out there that have apps in them. In the early days of personal computing, you didn't buy apps. Instead, you subscribed to computer magazines, and typed in the code they gave you for their app of the month. You can look for some of these and you might get some ideas. While they do give the source code, it's all in 1970's basic, and will need to be completely retooled for modern languages. Look for "Dave Ahl" and "basic computer games" will link to a book from the 1970 with, 101 ideas for apps.