locus
An energy oscillator — displace it, and watch energy move and return.
What it is
A locus is a point held by a potential — a field with a ground state it wants to return to. Displace it and it oscillates: energy pours from position (potential) into motion (kinetic) and back, swing after swing. With damping, each swing loses a little to the surroundings and the locus settles home. With drive, you do work on it and the energy climbs.
The ledger is the honest part. Total energy only rises when the drive puts work in, and only falls through damping. It never makes more than it's given. That balance is not a limitation — it's the same fact that guarantees a displaced system can always find its way back to ground. The math here is the engine under redtooth and the displacement framework: a ground state, a distance from it, and the cost of the path back.
Prototype. A real, energy-conserving oscillator simulation — single or double well, with damping and drive. It models how energy moves; it does not create it.