I am looking for an app to do something similar to what this guys are doing.
I mean, the customer can choose four products from our selection and then gets a discount. The customer can build up his own bundle with a fixed price.
Thanks in advance!
I recommend checking out the following apps as they have similar features to the example you showed:
Let me know if one of these helps. If there is anything else I can help you with, please let me know.
I'd recommend the PickyStory app for this. You can easily create bundles, let your shoppers choose specific products, variants, and add the pack with one click to the cart. It's also automatically applying your brand colors and style, so you only need minimum customization or none.
Here's an example of how it can look like:
Hope this helps!