The edition of the Greek NT prepared by Westcott and Hort has been the foundation stone of all modern Bible translation. It has been tweaked over the last 50 years by the German Bible Society, in its capacity of as a member of United Bible Society (UBS). In particular, they have carefully documented exactly WHICH manuscripts support a particular variation, e.g. the spelling difference between ἐκκακέω and ἐγκακέω in 2 Cor. 4:16.
Here is an example of a page from Philippians 3.
The UBS version of the GNT has been heavily used by the Wycliffe Bible Translators missions group as it has produced versions around the world, as well as by the translators of the RSV, NIV, ESV, and GNB in the English speaking world.
While many would agree that the Germans can be a bit idiosyncratic, it came as quite a surprise in 2009 when they started claiming to hold the copyright not just on their textual apparatus comparing manuscripts, but on the text of the Greek NT itself. That is to say, the German Bible Society has claimed a copyright on the precise words of Jesus and of Paul.
Christians, particularly those in the Internet world with an interest in Greek translation, were stunned. After all, you would think that after 2,000 years, the words of Paul would have entered the public domain.
But nobody wanted to let the world see us Christians squabbling over who holds the copyright on the words of Jesus. So rather than engage in a court battle, Christians withdrew the open source tools they had developed to help others study the Bible in Greek.
However, several members of the Society of Biblical Literature (SBL) said that this was nuts...and were determined to do something about it. Dr. Michael W. Holmes took the lead in preparing a fresh edition of the GNT, one that looked back to Westcott and Hort as well as to the translation committee of the New International Version (who started with the UBS GNT but made some judgement calls of their own) and came up with his own edition of the GNT...and did so just 18 months after the Germans/UBS made their copyright claim.
The UBS and the SBL versions both use Westcott and Hort as their starting point. So they have come up with editions that read very much alike. But since Holmes did not directly draw on the UBS version, he gets around their copyright claim.
In marked contrast to the UBS, the SBL has said that ANYbody can use their Greek version. It can be incorporated freely into other software products. It is available for free download.
Given the generous licensing arrangements associated with the SBLGNT, it has become ubiquitous on the web. It appears that the UBS GNT is slowly becoming marginalized. It will be interesting to see how they respond over the next few years.
One very positive development from the UBS is the publication of a Reader's Edition of the GNT. This is a hugely helpful edition of the GNT; one that the SBL cannot match at present. Perhaps the UBS will subtitle it "The Empire Strikes Back."