yWriter5 BETA, yWriter6 and yWriter7 are all identical in operation. They're just compiled for different versions of Windows. (yWriter5 and yWriter6 don't work as well with unicode character sets.)
** Mobile versions of yWriter are designed for editing your PC projects on the go, using Dropbox.
Or you might prefer to try Scrivener (not my software, but popular on the Mac)
The original Windows 98/XP version (yWriter2) installer is here just in case you have a YWP project from 20+ years ago.
(Use yWriter2 to convert from YWP to YW2, and then you can import the YW2 into yWriter 5 or later)
You can still get yWriter3 here here if you really need it.
I'm Simon Haynes, programmer and author.
Welcome to Spacejock Software
All my software is virus-free. No unwanted toolbars, trojans or other nasties.