I have been using one version of Nisus or another since 1994. I have written all of my academic work in it (it was one of the first to support right-to-left languages on the Mac) and while there was an annoying footnote bug that bit me when I was submitting my doctoral thesis, they have never been short of amazing in support.
Now Nisus Writer Pro 3.0 is out! I have not had a chance to play around much and review the changes, but everything continues to work well and smoothly, and its looking pretty too! Nowadays it has all the collaborative features you might want along with incredibly powerful tools. I am particularly excited about the following changes/updates:
• Split View, which allows you to:
○ show two or more parts of a document for simultaneous reading or editing
○ show or hide personal notes and pre-writing materials attached to your text
• Comments and tracked changes can be included in printouts and PDFs.
• Synchronized scrolling.
• Typewriter scrolling.
• Find and Replace matches can be shown as a results list, opened in a separate window.
It is reasonably inexpensive, it $65 for first-time buyers, $55 for academic purchase, and $45 for an upgrade. If you have bought 2.o in the last 90 days they will upgrade you for free. They also have a free 15-day trial so get it now (NB: that link is a direct download)! I receive nothing but good ju-ju from them for recommending their product, I just find it indispensable for my work.