Peff has released a free software synth ReFill for Propellerhead Reason, Monologue.
Here's what they have to say about it:
The Monologue Refill is a monophonic analogue synthesizer library for the Reason 4.0 NN-XT sampler. The sets include the standard sawtooth, square, triangle waves. Also included are a fixed rate pulse width modulation set, and hard sync sawtooth set. Other sources include, detuned pulses, frequency modulated oscillators, tuned oscillator layers, white noise, and sine wave samples from a self-oscillating resonant filter.
Download at Peff.com.