I was looking for an alternative diagram editor to Visio. I have been using Visio in the past but was looking for a better SaaS solution. I put my bet on draw.io, the alternative would be Lucidchart. It seems to have sufficient support for UML and plain ER diagrams. And it comes out of the box with Dropbox and Google Drive integration. Initial experiences are good. It responds appropriately. And I really like the Dropbox integration if offers! And no charges at all.