Unified Daughterboards - C4, C5, S1 The Unified Daughterboard Project is an open source project designed to standardize the USB daughterboards used in custom keyboards, spearheaded by many community contributors such as ai03. The goal of the project is to provide standards that are easy to build upon to incentivize DIY in the keyboard hobby, while providing an easy pipeline for replacements. Over the years, new additions to the project have been added. The current lineup consists of the S1, C4, and C5. The C4 and C5 are designed to fit into keyboards like the Bakeneko where the C3 was once used.