The following pages and posts are tagged with

TitleTypeExcerpt
I2C-23017 Page MCP23017 IO Expander with 4x IOB daughterboard connections
I2C-7311 Page I2C MAX7311/7312-based IO Expander with 4x IOB daughterboard connections
I2C-7313-cTc Page I2C MAX7313-based IO Expander cTc Wiring Harness
I2C-8574-cTc Page I2C PCF8574-based IO Expander cTc Wiring Harness
I2C-9685-PWM Page I2C 16 channel PWM Driver based on a PCA9685
I2C-AD4DA Page I2C 4x A/D 1x D/A I/O expander based on a PCF8591T
I2C-Codeline-Matrix Page I2C Slave - Codeline Matrix - DFRobot ProMini with 2x 8x8 LED Matrixes for displaying CodeLine packet content
I2C-Expander Page I2C PCF9555 / or / MCP23017 -based IO Expander with 4x IOB connections
I2C-LEDStripDriver Page WiFi/I2C LED Strip Driver based on a PCA9685
I2C-SignalTestJig Page Test Jig for simple signal panels
IO4-LED-Strip-Driver Page PWM Driver board for high current LED strips
IOB-I2C-MAX731x Page IOB I2C MAX7311/7318 based IO Expander

You are free to download these files and make your own boards.