The NA28 Greek New Testament is now available for purchase in Accordance Bible Software. The text itself is free here. The Accordance version includes the apparatus, marginalia, and other nice enhancements. Here’s a screencast that shows how you can use the NA28 in Accordance:
More about the Nestle-Aland edition is here. Its Accordance product page is here, with an Accordance blog post about it here.
Words on the Word 