With the capability to also work with digital signals, the SparkFun Analog/Digital MUX Breakout can be used to pipe TTL-level serial data to or from multiple devices. For instance, it can be used to connect the TX pins of 16 devices to a single RX pin on your microcontroller, allowing you to select any one of the 16 devices to listen to. For two-way communications, a second board can be added to route your microcontroller's TX line to 16 device's RX lines. By using multiple boards, similar arrangements can be created for I2C, SPI, and more.
The internal switches are bidirectional, support voltages between ground and VCC, have low "on" resistance and low "off" leakage. To prevent crosstalk, they perform "break-before-make" switching. The board also breaks out the chip's "enable" pin, which when driven high, will completely disconnect the common pin.
Key features of the SparkFun Analog/Digital MUX Breakout include a 2V to 6V operation, "On" resistance of 70 Ohms at 4.5V, 6ns break-before-make at 4.5V, and a wide operating temperature range of -55C to 125C.
For further information, SparkFun provides a schematic, Eagle Files, Datasheet, and a GitHub repository for the SparkFun Analog/Digital MUX Breakout - CD74HC4067.