Semaphore is a protocol, designed to be a simple and generic privacy layer for Ethereum DApps. Using zero knowledge, Ethereum users can prove their membership of a group and send signals such as votes or endorsements without revealing their original identity.
Bandada and Semaphore have different natures. Bandada is an infrastructure for managing on-chain and off-chain groups, while Semaphore is a protocol that allows you to cast a signal, such as a vote or endorsement, as a provable group member without revealing your identity. Bandada can use protocols like Semaphore to manage on-chain groups, as it currently does or use Semaphore libraries cast signals for off-chain groups.