Square

Square's interface lives on the merchant side of the counter, and that constraint shapes everything. The point-of-sale grid uses big photo-or-color tiles tuned for fast, glanceable tapping by someone mid-conversation with a customer. The signature moment is the handoff: the screen turns toward the buyer, who taps, tips, and signs on the same device, so the terminal becomes a shared object. Tip prompts are deliberately prominent, a choice that helps sellers and has drawn fair criticism for pressuring buyers. The receipt step, email or text or skip, is clean. Behind the counter, reporting and item management are competent if utilitarian. Square's enduring strength is treating a transaction as a two-person interaction and designing the device to be passed across, not just operated.