I tend to use Google Keep (https://keep.google.com/) for this sort of thing, which is similarly pretty lightweight and doesn't impose much structure on anything, but is also permanently backed up and synced between all platforms, with nice mobile apps, and a simple URL you can just type for the web.

It also has some extra support for lists, which is handy for many of the sorts of things that it gets used for, and can handle images to some extent too.

[The one thing I wish it did was some sort of background version control, so when I accidentally delete something important I can get it back...]