A treasure of knowledge as posted on blog.reprap.org was collected by Gary Hogdson, which I host here as well for archival purposes:
- A History of RepRap Development (2012) (PDF, 1790 pages, 47MB, GPL License)
2005-2011 posts by Adrian Bowyer, Vik Olliver and others
Early research for
- extruders, nozzels, heating blocks
- printing material research ABS, PLA and other materials
- slicing algorithms
- deciding to use Arduino as motor controller
Notable Excerpts
RepRap Family Growth
Adrian Bowyer summarizes RepRap history April 18, 2011, in brackets the amount of RepRaps:
- Spring 2007 – The first RepRap Darwin was finished. Its RP parts were made in a Stratasys Dimension. [1]
- During that summer we made four or five sets of parts for the machine in the
Stratasys and sent them to RepRap team members round the world. - September 30, 2007 – Vik Olliver in New Zealand finished the second Darwin. [3]
- Around Christmas 2007 – A number of people start to make wooden and lasercut copies of Darwin. The Bath RepRap Lab also supplied a Stratasys-printed set of Darwin parts to Ian Adkins of Bits from Bytes, who created silicone moulds from them and started selling Darwin copies made by PU moulding. [8]
- February 21, 2008 – Zach Smith (now also of MakerBot) gets his Darwin working. [20]
- February 22, 2008 – Ponoko have a lasercut version of Darwin.
Spring 2008 – Lots of the wooden and moulded Darwin-type Repstraps are working, and people start using them to print RepRaps. - April 2008 – Nophead starts printing Darwin parts on his Repstrap Hydraraptor. [60]
- May 29, 2008 – Vik Olliver’s Darwin has made a full set of parts for another
Darwin; these are assembled in New Zealand and finally tested when he visits at Bath University in the UK. This is the first true RepRap replication. [100] - Summer 2009 – RepRap Mendel introduced. [400]
Around this time Nophead, I, and many others went into serious production
selling reprapped sets of parts for RepRaps made in RepRap machines on Ebay etc. Summer 2010 [1500] - Spring 2011 – Nophead alone has made over 100 RepRaps for other people. I have made over 50. [4000]
RepRap Darwin (2007) 
RepRap Mendel (2009) 
RepRap Huxley (2010)
Prusa Mendel Announcement
October 4, 2010 Josef Prusa announced his “Prusa Mendel“ version with this post:
He eventually iterated to “Prusa i3“ May 2012, which became quasi standard for low-cost FDM 3D printers.
Prusa Mendel (2010) 
Prusa i3 (2012)
See also 3D Printer History.