Overleaf is a collaborative writing and publishing system designed to make the process of producing academic papers much quicker for both authors and publishers, from Writelatex Limited in London.
Overleaf is great for writing scientific and research documents, especially when there is a lot of technical detail and mathematics involved. It shines when using complicated formats such as double column, or changing font sizes and still maintaining professional looking formatting. One of the best features is the collaborative writing with people in your team. You can work on a document together, leave notes and comments for the other person to read, and if you have the paid subscription the version history feature is great. The only time I think Overleaf is not suitable is when the document complexity does not justify it - for a simple document without mathematics and just a few paragraphs, or a rough document which does not need to be shared - a simple Microsoft Word document will be better
If you're doing any sort of text editing, you should consider Vim--once you climb the learning curve, you'll be faster and more efficient at everything you do. Also, Vim is my default search/replace tool--whenever I need to make changes throughout a document, most often, I'll copy and paste into a Vim window so that I can take advantage of regexp-based replacements. Vim isn't for the faint of heart, though--it's hard to learn and super complex. If you use a text editor once or twice a month, or just need a simple way to strip out formatting, Notepad will get you where you want to go without all the confusion.
It's easy to use for a variety of skill levels. It has most features you could want from an text editor and LaTeX editor. Collaboration is easy for all skill levels including for first time users. The UI is pleasant enough and the website is quick to load. All the packages you need are available.
I don't consider the steep learning curve to be a hinderance on the overall usability. I would rate this a ten, but to be honest a lot of people do get hung up at the beginning and just abandon it. However, for people who have made the moderate effort to get over the hump, nothing can be more usable.
The support is somewhat lacking; Vim doesn't really have support outside of its forums. The forums, while notably good, aren't equal to real support though, and the steep learning curve makes you wish there was a help desk that would assist with all of the basic questions. There are several handy books and guides that can be found, and most implementations of the product come with "vitutor" which walks you through its usage.
Alongside Overleaf, we have tried using Microsoft Word and Google Docs to write reports. While they all let you write in the same document at once, Overleaf just works better for us. Microsoft Word locks the paragraph someone else is working on to avoid others messing with it before the original writer is done. However, it is often slow to open those paragraphs up for others to edit. Google Docs is the hardest one of them to make a good layout on, though with the app, it can be good for proofreading on the go.
I think it comes down to usability (and frankly, just preference). There's an old adage that Emacs is a good Operating System with a poor Text Editor! Jokes aside, when looking at different text editors, such as Emacs or Nano, Vim is the one that is usually always preferred because of how simple it is to learn. The learning curve of Vim compared to other text editors just makes it such a natural choice.
