Julie here from Shopify Support.
It's great to hear that you're looking to implement a referral program. This is a great way to boost customer retention and build a community around your brand.
While there are quite a few referral apps in our App Store, I recommend checking out Secomapp: Affiliate Marketing and Conjured Referrals. Both of these apps allow you to create unique referral programs and integrate with a number of email marketing apps to help you promote your referral program. Taking a look at the app descriptions, I can also see that these apps give you the ability to create a "Give X, Get X" type of referral with discount codes and gift cards. They both are highly customizable and also offer in-depth analytics so that you can see which referrers are performing the best.
Both of these apps have great reviews and are quite popular. I recommend taking some time to explore both. From their respective About pages, you can also view their feature list, reviews, and screenshots, which will give you a good idea of what the app looks like. Under the Support section in each app About page, you'll also be able to access the developer's website, along with their FAQs. They also offer free trials which you can take advantage of; just make sure to uninstall whichever apps you no longer wish to use prior to the trial expiring so you won't be charged.
As you continue working on implementing a referral program for your business, I recommend checking out our blog post, "Referral Marketing 101: 7 Tactics to Launch Your Own Referral Campaign". This post covers the basics of referral marketing and includes some examples of successful referral marketing campaigns, along with some steps you can take to build your own powerful campaign. I think you'll find it quite useful.
I hope this guides you in the right direction! I'd also love to learn more about your plans for your referral program. Are you wanting to provide referrers with store credit or free products? If you can provide me with some more information about what you're looking to accomplish, I'd be happy to pass along some further resources.
Looking forward to hearing from you!