2 Channel Gain is a simple stereo audio or dual cv level control, with a small footprint to easily squeeze alongside the source which it is trimming/amplifying.
The THRU input offers post-fader summing, so units can be daisy-chained from OUT to THRU of the next unit, without signal degradation. This simplifies wiring, and acts like a decentralized mixer for clearer organization. Chains can also be sent to the input of a successive unit, allowing it to act as a bus/master fader. It's very flexible and promotes organization.
For a feature-rich version, which can be cv controlled, see the Addition Fader.