Every Black Friday, tons of apps go cheap or free on the App Store. I always use this opportunity to score a bunch of apps I have been waiting on, particular higher priced apps.
The best resource I have found for keeping track of every deal is MacStories. Check out their blog post on The Best Deals for iPhone and iPad Apps, Games, and Accessories. They have already started collecting apps on sale and will be updating it all throughout tomorrow and in the coming days. It catalogues apps ranging from iOS apps to Mac apps to tech deals on Amazon.
Happy app purchasing!!!