Wurr Audio has released GreenMachine Amp II, a Windows VST guitar amplifier, as a free download.
GreenMachine offers a huge number of options:
The main design philosophy behind the GreenMachine II is to make it as controllable and flexible as possible. We believe that continuous parameter control is much more powerful than having a list of options on a drop down list (i.e. a list of "amp models" or "cabinet types"). So, this plugin may offer less options at a first glance, but it offers much more in-depth adjustment possibilities. For example, while there might be only three cabinet types in GreenMachine II, there are five continuous parameters to customize the speaker simulator response, instead of maybe only a pesky "dynamic/ condenser mic" switch.
Wurr Audio has also released a a virtual stereo tube preamp, reverb and EQ filter as free downloads.