Super useful, extremely affordable.
The Nady MM-242 4-Channel Mini Mixing Console has 8 mono 1/4" inputs with individual volume controls that can be assigned to one mono output or grouped to separate stereo outputs. Stereo 1/4" balanced TRS master outputs feature separate master volume controls for each channel, up to 25dB of gain, S/N ratio of 85dB, and 10Hz to 100kHz frequency response. Mono/stereo mode selector switch determines whether all the inputs mix to one 1/4" out or to stereo outs. Power on/off switch with an LED indicator. This affordable audio mixer runs on 9V battery or optional power supply.