When you experiment with the Raspberry Pi on a regular basis and you connect a variety of external hardware to the GPIO port via the header you may well have caused some damage in the past. The Raspberry Pi Buffer Board is there to prevent this! The board is compatible with Raspberry Pi Zero, 3, 4, 5 and 400.
All 26 GPIOs are buffered with bi-directional voltage translators to protect the Raspberry Pi when experimenting with new circuits. The PCB is intended to be inserted in the back of Raspberry Pi< 400. The connector to connect to the Raspberry Pi is a right angled 40-way receptacle (2x20). The PCB is only a fraction wider. A 40-way flat cable with appropriate 2x20 headers can be connected to the buffer output header to experiment for instance with a circuit on a breadboard or PCB.
The circuit uses four TXS0108E ICs by Texas Instruments. The PCB can also be put upright on a Raspberry Pi 3 or newer.