I actually specifically chose Zotero over Mendeley because Mendeley is owned by Elsevier. Their company has always been a toxic influence on publishing.

Recently they even added a new dark pattern so that when you click the "download PDF" button on their articles it opens up a web app reader loaded with tracking instead of just giving you a PDF. You then have to spend time and click through about three menus to really download the PDF.

It's to the point that I avoid articles published by Elsevier if possible. Easier in my field than others I'm sure.

I agree that Elsevier is toxic, and wish they didn't own Mendeley. Unfortunately, at least the last time I compared them, Mendeley was way better than Zotero for my personal use and just couldn't use Zotero. The cloud sync and sharing, the lit search, and all were just so much more compelling. I do think its been long enough I might poke at Zotero again and see if its caught up.

I used Mendeley to keep track of papers during my PhD. It was really a fantastic piece of software.

Too bad they sold out to the dark side. After they were acquired, I switched to Zotero, but I wasn't doing active research anymore by then, so I don't have as much experience of using Zotero. On the surface it looks pretty good though.

It should be noted that Mendeley encrypts user database, presumably to lock in its users: https://eighty-twenty.org/2018/06/13/mendeley-encrypted-db

Does it have any kind of export functionality at all?

It does, but it's only partial - it'll only export the basic stuff.

You can export to BiBTeX (.bib).

You lose your folder organization (a.o.) that way. There used to be a direct import of the database into Zotero (much like Mendeley can do direct import of Zotero DBs) but that has become impossible since Mendeley have encrypted their database, for which they hand-wave to an unspecified GDPR article that apparently forces their hand, but not Zotero, Excel, or a million other apps that you use to process your own data. Plenty of people have asked Mendeley on Twitter to clarify exactly what article would compel this over the past two years, with not a single public response by Mendeley.

This is one of those cases where the "evil" side has a superior product. Imagine if Elsavier were a little nicer.

I reluctantly switched from Zotero to Mendeley as Mendeley has Android app that synchronises highlights, notes, read-progress etc. with the desktop version. It made reading papers on my tablet a delight.

I use zotero and store the pdf files (renamed and organized with ZotFile) on OneDrive. I can read papers and make highlights/notes to pdfs and they will sync to all of my devices. These notes can be extracted and made searchable within Zotero by Zotfile.

At first I preferred the way that Mendeley did this with its built in pdf reader, but now I'm happy Zotero delegates to the pdf software of your choice.

If you were on the iPhone mac side, papers had a brilliant solution that was appealing

Is Mendeley free? I couldnt easily tell from the website. Also, which is better for non-academics, who just want to organize areas of interest/notes?

lastly -- how good is their mobile app?

Mendeley and Zotero are both free, but both have storage limits beyond which you have to pay (Zotero is 300M, Mendeley is 2G). If you only store references and annotations you'll likely never exceed those limits, but if you use them as a paper archive you may. (I have a 3G archive)

To clarify, Zotero's storage limit is only for syncing of attached files. You can use Zotero entirely offline if you choose, storing as much as you want, and we also support WebDAV or linked files (which can be in Dropbox, etc.) for syncing files in your personal library.

(Disclosure: Zotero developer)