If you don't care about a small amount of detritus then the easy way to uninstall the program is to simply move its program folder (wherever you installed it) and its data folder, /boot/home/PineappleData, into the trash. However if you want to get really serious about it this help topic will give you all the information you need to remove the remaining traces.
Remove old message files Since it's possible to drag message files out of the program they might be scattered all over your hard drives, if you are prone to that kind of activity. Use the Find utility from the Be Menu to locate and remove all files of type Pineapple Message.
Remove all file types and BFS indexes Pineapple News creates two file types, text/Pineapple Message and text/Initialization file, and one BFS index, PINEAPPLE:msgid. You can remove them manually using the FileTypes preferences app and the command-line program rmindex if you like or you can get the program to do the job for you. To make the program do it, open a Terminal window, navigate to the folder that contains the PineappleNews executable file, and issue the following command:
PineappleNews /uninstall
Once you've done that you should immediately erase the program because if you run it again it will re-create all the stuff it just removed.
Remove PineappleNews.ini The program's settings file is located at /boot/home/config/settings/PineappleNews.ini. Delete it.
That's it, you're done.