In a recent podcast, I took up the topic of online writing tools and what they can, and cannot, do to help you with your writing. What is out there? What might help you?
Let's get started by establishing some baseline ideas about writing. First, writing is a process, that is iterative (repeated) and social: you write, largely, to communicate with others. One more thing: Writing is genre-driven, which means that there are types or kinds of documents that are used to accomplish a variety of specific purposes (resumes are a genre that serves the social purpose of getting hired). At first glance, it isn't clear how online tools can help with those aspects of writing.
We also need to consider the sub-skills that contribute to good writing performances. To write well, you need to understand your writing process and what would help you at each stage of the process. You also need rhetorical knowledge: who are you writing or communicating to and for what purposes? Do you understand and have experience writing the kind of document (the genre of document) that your communication situation calls for? And finally, do you know enough about the topic to write well about it?
So, what online tools can help? At the early stages of drafting a document, some sites can help you add to your subject matter knowledge base. Because these are specific to each person and context, I can't really link to any. But Google Scholar will connect you to academic research, and other sites and search techniques would also help.
After you have a draft, grammar and spell-checker software can help you with sentence-based grammar and spelling. Grammarly is one popular tool; GradeProof is another, free one (an add on for Google docs). There are many others, some of them free. Check out the many reviews to find something that fits your needs and budget. But try to select something that not only corrects the errors but also explains why the correction needs to be made at all.
A key component of improving as a writer is feedback: how can you get it? You might use LinkedIn and Twitter to follow others with a similar subject matter interest or writing consultants that might give answers or advice if you are one of their followers. You could also search out hashtags that identify strings of posts that might help you with a writing issue.
Most important, though, is joining a writing community or finding others who are working on similar documents. If working in a large organization, perhaps you could connect with others in your organization. That would sidestep the problem of sharing work-related documents outside of the organization, and it would help build your network within the company. Writing well depends upon excellent reading skills; if you exchange drafts with others in your organization, you can learn an enormous amount about how to write well from reading and offering comments on those texts. Google Docs, Dropbox, Word, and other file sharing software applications that offer the ability to comment on documents are all tools that can support sharing and commenting.