I've built one as well, it's https://www.gonevis.com, would like to know your opinion on it as a person that built a similar service.
nice, will this be open sourced ?
Thanks! For now, I don't think so.
but you said "not be tied to any platform." on the landing page? Will the blog be hosted on your platform? or it has on-premises install?
Yes, but all the content will be stored in Markdown (which is highly portable format), so you'd be able to download all your posts and switch at any time. And by blogging on your own domain you would be the owner of your traffic and SEO ranking (unlike writing on Medium).