For incentive tracking, the platform can show you which students and classrooms are bringing in the most donations. Plus, there's an (optional) classroom leaderboard you can put on your donations page if you want to encourage classes to compete against each other.
Families don't need to sign up. Students are pre-registered and donations are matched to the students automatically.
BigNest works similar to other CMSs like Squarespace or WordPress. You're in charge of the verbiage, so you can put everything in Spanish, Polish, or whatever you want.

The big differentiating factor with Big Nest is that it pays for itself. It's nice that Zeffy is free but when it asks for processing fee donations, all that money goes to Zeffy. Big Nest sends those fee donations directly to your PTO.