*briefly un-lurks*
Well, if all you're after is a drop-in, super-similar replacement for Word, you should look at
LibreOffice. It's meant to be compatible with Microsoft Office's file formats and is laid out in a nearly identical manner, and it's completely free. Also comes with spreadsheet software (replacing Excel), presentation software (replacing Powerpoint), and a few other things, so if you also need other office software for work or school or something then LibreOffice should have you covered there, too.
Other options:
-If your new computer is a Mac, I think Apple's own word processing software, Pages, is either free or cheap in the App Store, and it's also pretty similar to Word in function, albeit with a very different layout.
-A lot of people write entirely online in Google Docs, so if you have or are willing to create a Google account there's that.
-Personally, I do a lot of note-taking and shorter writing in plain old text documents, lightly formatted with Markdown. I like them because I don't usually need all the bells and whistles of a full word processor, and because .txt/.md files are just about the simplest thing to move between different computers (I have both a PC and a Mac and bounce between them regularly, and back in college I was also frequently writing on the school's lab PCs/Macs) because it's impossible to find a computer that
doesn't have at least a basic program that can open them. I don't actually write in Notepad, though; I use a text editor that's intended for code because I'm a giant nerd, more or less. (For other nerds who might happen to wonder, right now I'm specifically using Visual Studio Code, but I've used Sublime Text, Atom and Brackets as well; Brackets was my previous favorite.) For non-nerds, Notepad will work just fine as long as you turn on the word wrap setting.
-Recently I've been trying to write my longer fics in Scrivener. Scrivener is not free (but not that expensive, either, especially if you can get it with a discount code after completing a NaNoWriMo event if NaNo's your thing), and it's far more bell-and-whistle-y than a standard word processor, but it's intended specifically for authors and comes with some built-in organizational features and such, like the ability to break your story into sections without needing separate files. I am a deeply disorganized person who can't write more than a sentence of fiction without a plan these days, so as I play around with it and write more in it I'm finding it helpful for visualizing things and keeping them in more manageable chunks. It's definitely overkill if you don't need that sort of organizational hand-holding, however, and again, not free, so that might be a factor, idk.
-I used to use/occasionally still use any of several "distraction-free" writing programs, which basically take over your whole screen with nothing but your story so you're not distracted by the rest of your computer/any fancy word processor options. Most of them also use .txt or .md files as their format. There are tons of these things, but for example you could look at FocusWriter or Writemonkey or Cold Turkey Writer, all with varying appearances and degrees of
forcing you not to touch Facebook during writing time rather than just hiding it from you.
There are countless other options out there; these are just the ones I believe are most common/the ones I often use. It's kind of hard to go wrong when all you need to do is write words, save those words and copy and paste those words into Serebii's post editor! If you're at all interested in experimenting with something other than "as close to Word as possible", you can't go wrong with just grabbing a bunch of the various free options or a Scrivener free trial and playing around with them for a bit to see what you're most comfortable with--as long as it's easy to use and gets out of your way when you need to
write, it's a good 'un.
*re-lurks*