Small, simple, useful. The multiple is the simplest utility you can find, it lets you split a signal in two, or combine two into one. Works in any direction or combination. These are passive, so voltage will be halved when split, which can be useful when sending modulation but is not ideal for precise voltages such as pitch information. Great for combining modulation or sending the same modulation to two separate destinations.

When combining voltages, please make sure the receiving module can handle the final combined voltage output. Know your gear!