To take advantage of the large luminosity-resolution product of the Fabry-Pérot interferometer used in tandem with modest-aperture telescopes, a Fabry-Pérot interferometer has been developed that is widely adaptable to a variety of extended source observations. The instrument is designed for adaptability across a range of optical and near-IR (NIR) spectral lines from 550 to 1100 nm, which are characterized by a wide range of velocity distributions of the emitting species. The system features a twin-étalon configuration to provide an extended free spectral range and to enhance contrast when observations include bright reflected solar or twilight backgrounds. Although the optical path and all the optical elements of the system are readily accessible, the instrument is ruggedized for transportability and extended remote field operation once it is optically configured. State-of-the-art, modularly adaptable, proven detectors (GaAs photomultipliers, large CCDs, and germanium integrating detectors) are featured to optimize instrument sensitivity. Recently, a series of NIR observations were made at the Millstone Hill Incoherent Scatter Radar Facility, Westford, Massachusetts, in a single-étalon mode.