OkaiR2R is an emulation based on the preamp section of the AKAI X-100D reel-to-reel recorder.
It models the germanium transistor based preamps with optional NAB equalization as well as the output transformers used for the headphones. When the preamps and/or transformers are pushed they will distort the audio in the same analog non-linear way as the real thing.
The low- and high-end response changes accordingly as well, giving that warm vintage touch to your audio.
OkaiR2R also has an accurate reproduction of the VU meters with the same response to audio signals.