The creators of Twitter have created a Tumblr-esque sharing platform called Medium. You can sign in with your Twitter account and let them know you're interested in sharing. It is supposed to let the most interesting things rise to the top as it is curated, but it really looks quite a bit like Tumblr. I don't have posting rights yet, but I did sign in and ask for them. If you follow new technology, this is one to watch.