In addition to adding, removing, and editing groups, you can also add and remove group members. Just select a group and then tap on the Add Contacts to Group button and you are off to the races. It was all very intuitive and, as a Beta testor, I was witness to the hard work the developer went through to make it as easy as possible for users. For instance, to remove a member from the group, just tap on the "X" button next to their name.
A nice touch is the ability to see all of the groups a specific contact belongs to. From that view, you can use checkboxes to add and remove that member from specific groups in the same screen. This is another feature I would like to see on the Mac.
Somewhat related is are Interact Operations. Using groups of selected contacts, you can perform actions on them like deletion, group creation, adding to existing groups, and even sharing groups of contacts’ vCard information.
Don't forget that Interact is made by the same guy that brought us Drafts. You can see this lineage with the Scratchpad feature. Using the Scratchpad, you can copy text including address and contact information into the application and it will automatically parse that out into contact data that can be added to an existing contact or create a new one. There is even an extension so you can select text in some other app, like your email client, and automatically send it to Interact to perform its magic. This is a great feature, which the developer screencasted right here to explain. In all of my years of using iOS, I’ve never seen a faster way to grab unformatted contact information and add it to my contact database. Because Interact works with the same database as the native Contacts application, any data you add in Interact populates across your device and back to your Mac.
The whole experience of using the Scratchpad reminds me a lot of the first time I started using Fantastical to add calendar appointments. No longer am I forced to constrain myself to the requirements of the computer. Instead I just give the computer data and it does the work for me. I love this feature and now I wish I had it on my Mac too.
Interact also has a clever sharing feature called Context. This is a way to access your contacts from other applications. If, for instance you have a bit of text you want to send off to multiple family members as email or a text message, you can access the Interact Context feature through the iOS share sheet. Tap on the Interact icon and it gives you a list of your groups. With the above example, you could select your family group and then individually select the specific members to receive the message. Then you can tap on the mail or the message icon and Interact opens up the appropriate application with the text copied in and the selected contacts already in the addressee line. In short, it lets you take bits of text and easily send them off to people from your contact list. I did mention this application was from the same guy who made Drafts, right?
I think the earlier analogy to Fantastical sticks. Interact brings a lot of utility and power to contact managers that I simply haven't seen before. You can learn more on the website or in the App Store.