Another good choice is the Paraphrasing Tool, a free tool with four paraphrasing modes and 15 languages. It's fast and accurate because of its AI algorithms, and it's secure because it automatically wipes its database of your content after you're done. It's good for writers, bloggers and students who want to improve their writing's readability and avoid plagiarism.
If you want something more flexible, Paraphrase Tool offers a tool that works in more than 100 languages. It's got a compose mode for writing fast and a plagiarism detector, too, so it's good for writing articles, cover letters and essays. It also offers a 3-day free trial if you want to try it out.