What are the differences between a V0, V1, V2, Switchwire, and Legacy?

[Demosth]

I'm so confused. Does the "V" stand for version? Why would anyone do version 0 if version 2 is out?

[Demosth]

The "V" stands for "Voron" Each printer has its benefits and advantages and slightly different build complexities. 

V0
Voron0 is a traditional coreXY design with the bed moving along the Z axis. It has a tiny 120mm^3 print area, and is built with 1515 extrusions. It encloses naturally, so printing ABS is possible. Currently, all single mechanical parts for V1 and V2 can be printed on a V0 bed.

The design accounts for stock Makerbeam XL extrusion lengths (which come tapped) and standard MGN7 linear rail lengths, so scaling the design will start to increase cost or labor involved with tapping. The bed is also cantilevered which will also restrict scaling. This printer can be built for around $400 USD. https://github.com/VoronDesign/Voron-0/releases/

V1 
Voron1 is a traditional coreXY design where the bed moves along the Z axis. It is simpler to build compared to V2 and can be built for around $1,000 USD. It encloses naturally so ABS or other temperature sensitive filaments can be printed easily. It uses rails for the X and Y axis so you can scale to a 300x300 plate. Z height is somewhat restricted due to the limited options with integrated lead screw steppers. https://github.com/VoronDesign/Voron-1/releases/

V2 
Voron2 is a modified coreXY design with a static bed and a gantry that moves along the Z axis. It is a much more complex build because it includes things such as 4-point gantry tramming to align to the print surface, dual MCUs, and other unique features. It is also designed to be fully enclosed so it prints ABS or similar filaments very well. Due to the linear rails the design is scalable all the way up to 350^3. More linear rails, larger print surface, and other V2-specific items make this printer more expensive and totals up to around $1,500 USD. https://github.com/VoronDesign/Voron-2/releases/

Switchwire 
Voron Designs take on a classic Mendel (aka "bedflinger") design. It is a CoreXZ design so the print head is belt-driven in both the X and Z axis, eliminating the typical leadscrew Z drive. This allows for very fast Z movement speeds and less weight on the gantry by moving the X motor to the frame. The stiff 3030/3060 constructed frame is just large enough to cover the entire swing of the bed and allows for a natural enclosure. This printer should cost around $600-800 USD brand new but this price could be lowered by leaving off an enclosure or reusing spares you might have lying around. https://github.com/VoronDesign/Voron-Switchwire/releases/

Legacy 
Legacy is a reimagining of the original VORON. It maintains the aesthetics of the original machine, while updating it for 2020. If you have a rod-based VORON (1.0/1.5/1.6) you'd like to upgrade but aren't ready for a total linear rail overhaul that 1.8 offers, Legacy is a perfect option. If building new, it allows one to relive the beginnings of VORON in both assembly and operation without giving up the Afterburner ecosystem or regressing to using RAMPs electronics package. It's also the lowest price full-size CoreXY platform we offer at around $800 USD. https://github.com/VoronDesign/Voron-Legacy/releases/