Artifake_Labs has introduced a free virtual Mellotron for Windows, Redtron_SE.

Features:

• Nine sound types : MKII Flute, MKII 3 Violins, M400 Cello, MKII Brass, M400 Combined Choir, M400 String Section, M400 Woodwinds, M300A Violins, M300B Violin.
• No loops : as the original Mellotron, each sound is eight seconds long with, in many cases, “the bad endings”.
• Exclusive “Mellotronic Click” switch. On real Mellotrons, “Click” can be heard at the beginning of a note, when the tape comes in contact with the replay head. These “clicks” are here randomly generated, so you don’t hear twice the same and they can appear on any key ; A rotary knob allows you to control the effect intensity (of course, you can also completely disable it ). Note : this function is inactive when the attack parameter is set to any value different from zero.
• Layer (two sounds A & B) and split possibilities (octave shift).
• Independent parameters for sound A & B :
  • Volume, Tone, Pan, Tune, Reverb, Delay, Attack & Release, Octave & Note parameters.
  • Delay effect (Amount, Time, Feedback & Pan parameters).
  • Reverb effect (Mix, Width, Size & Damp parameters).
• Global Volume control.
• Global Tone control.
• Global Pitch control.

According to the developer, “Redtron_SE is probably the most faithful and authentic Mellotron’s emulation of all Redtron Plug-ins.”