Jetted Narrow-Line Seyfert 1 Galaxies & Co.: where do we stand?
  The discovery in 2008 of high-energy gamma-rays from Narrow-Line Seyfert 1
Galaxies (NLS1s) made it clear that there were active galactic nuclei (AGN)
other than blazars and radio galaxies that can eject powerful relativistic
jets. In addition to NLS1s, the great performance of the Fermi Large Area
Telescope made it possible to discover MeV-GeV photons emitted from more
classes of AGN, like Seyferts, Compact Steep Spectrum Gigahertz Peaked Sources
(CSS/GPS), and disk-hosted radio galaxies. Although observations indicate a
variety of objects, their physical characteristics point to a central engine
powered by a relatively small-mass black hole (but, obviously, there are
interpretations against this view). This essay critically reviews the
literature published on these topics during the last eight years and analyses
the perspectives for the forthcoming years.
