From KVR Audio:
AXP SoftAmp 3OD is a Vacuum Triode Stage simulator. A single triode stage circuit typical for guitar preamps is captured in this plug-in. The model engine is based on a system of non-linear ODEs. Some smart calculation techniques are used to reduce the computational load. This effect could be used to apply mild tube overdrive to add some presence to your tracks, or you could chain a couple of instances together for a full-blown high-gain overdrive. The plug-in UI has a real-time transfer characteristic plot display. It provides an overview of the things going on inside the tube. It also has a peak-detecting algorithm that will flash a line when the level exceeds 0dB. You can monitor stereo channels separately or at once by clicking the corresponding buttons under the plot display. 16x switchable oversampling is also implemented to reduce the aliasing effects.