I've been using yWriter 5 for a couple of years. (I didn't know there was a new version out, although from the description 6 looks to be identical to 5).

I find it very useful for keeping track of facts, especially related to characters. When I start writing about a new person, I add their full name to the character database, as well as their role in the story. This is especially useful for minor characters where they may appear briefly several times throughout a story. When I forget to add them to the list, I keep having to refer back to the earlier chapters to get their names correct.

It can also keep track of objects and places, but as my stories tend to focus on people, I don't use this functionality very often. It also has a function for assigning dates/times to scenes, but again, I haven't bothered with this function.

The software encourages you to split your work into scenes. I find this useful when organising a long story (and most of my stories end up being long). Because the software keeps track of the length of each scene, I can split the work up into chapters, and then if I find that the lengths are varying to much, shuffle scenes between chapters to balance the chapter length. By giving each scene a short description I have an overview of the story as a whole.

Having the work via scenes also means I can easily skip a scene and come back to it later. Although I tend to write in a linear fashion most of the time, it is sometimes handy to be able to write out of sequence, and the organisation of the software means I can do this without trying to find the right point in a long document.

It does lack a few features that would be useful. It's spell checker is very basic and it doesn't have a grammar checker. For these functions I tend to use Word, as I haven't found a better alternative. What the software does have is the ability to export and import the story so that you can edit it in other software, or send to an editor for review. As long as you don't delete the embedded scene and chapter markers it inserts, it will round trip to other software successfully. You can also tell it to use any software as the scene editor if you don't want to use the internal editor.

The other thing I do is have the computer read the text aloud to me so I can pick up where I have used the wrong word in a sentence, something that can be missed by spelling/grammar checkers alone. It would be nice if it had this feature, but instead I use the import/export to temporarily transfer to dedicated screen reader software.

The slightly annoying thing is that everything is saved as RTF, which although a common format, is slightly dated and becoming less supported in newer software. Internally each scene is saved as a separate file in a project folder, and I sync these between computers through Google drive. This allows me to edit the files on any machine, except for my Android devices, as I can't find a decent app that will edit RTF files. Google Docs insists on converting everything to the newer DOCX format.

While this is primarily Windows software, it will work on Linux with a bit of persuasion. I have an old Dell netbook that I use when I want to sit and write outside in the garden, but it is exceedingly slow under Windows. I have set it to dual boot to Linux, as that runs quicker, and have successfully managed to run yWriter, although it wasn't 100% stable under that setup, so needed to make sure to save regularly or risk losing work.

One feature that has saved me on occasion is that it will automatically backup up your work into zip files at regular intervals. I have accidentally deleted work before and been able to retrieve it again later from the backups.

Overall I like the software and haven't found anything I prefer better as a replacement. I did try and find an open source alternative that would work better on Linux, but couldn't find anything I liked. I have tried Scrivener, but didn't find it any better and was put off by the $40 price tag. I write for a hobby, so if I'm going to spend money on it I would rather support the Hatbox instead.

I would recommend trying it out. If you find yourself having to write notes or constantly look back through previous work for character details, then you will find it useful. Also, if you are writing in chapters and sharing with editors, the ability to flag the status of individual scenes/chapters as to how far through the edit process they are may come in handy. It is written by an author for himself and other authors, and as such contains a lot of useful features that could come in handy. I don't use a lot of the tools, but it's handy having them should I need them.