1Password is a password manager, it used to be on just OS X, then OS X and iOS; these days also on Android and Windows. Plus anything that runs Firefox or Chrome. The legit versions that can install extentions.

There are two kinds of borwser extentions for 1Password, there are "1Password" and "1Password X". The main differnece between the two is that the latter is a full client that doesn't require the desktop app to work. This has the added advantage that 1Password X works on Chrome OS and Linux.

I have used both of them a lot, and mostly used X over the last few years. These days they are more or less the same. In the past the user experience was better on X.

Agile bits also works on a Linux version of their Desktop app, so I guess I won't need X for my use.