Write & Improve is 'non-native speaker first' - it is designed exclusively for non-native speakers, based on non-native speaker training data and analysis of non-native speaker needs.
Write & Improve provides principled English Language Teaching content, offering a library of hundreds of essay prompts either from Cambridge English or written to reflect them, across multiple levels of proficiency, and encourages the learner to seek progress to a higher level in their writing generally. Other tools focus on the current piece of writing only and do not seek to teach. Write & Improve is a practice environment, while others are for 'fixing' individual pieces of writing.
Other tools try for full coverage and go beyond 'errors' to try to cover elements of writing that are really questions of style or personal choice, rather than errors. This can be confusing and problematic for learners. Write & Improve, on the other hand, is very cautious about saying that something is wrong - both in that it only marks something as a possible error if the system is at least 90% certain that it is one, and in that it does not seek to give feedback on every single 'error'. Its feedback is also worded in a way that is designed to make the learner reflect on what they have written and make *their own decision* about whether they need to make a change.
W&I gives a variety of different types of feedback - summative (the CEFR score), formative (the teacherly encouragement, or motivational feedback), a progress graph to visualise stages of development, word-level feedback, sentence-level feedback, and a prompt relevance score. Other tools give only error feedback, without scoring or encouragement or any attempt to show progress and improvement.
Because W&I provides a CEFR score, learners are able to benchmark their achievement against other learners all over the world. Other writing tools don't do this.
Because W&I provides motivational feedback and a progress graph, learners are able to compare their achievement on their current piece of writing with their own previous work, to see that they are improving. Other tools do not provide an insight into personal progress.
Write & Improve is aimed at helping learners to become better writers of English and better editors of their own writing.