I need to draw a lot of block diagrams for my personal notes everyday. They are nothing fancy, just a few blocks with text in them connected with lines or curves. There are many drawing apps out there that let you draw rectangles and lines, but the problem comes when I have to rearrange them. They can't just be dragged and dropped elsewhere. I have tried Omnigraffe, but it is way too expensive and I will be using only 1/10th of what it offers. There are also a few cross platform java apps for this but they don't feel very responsive. Currently I am using Preview to do this. I open an all white image in Preview and use it's annotation bar to draw shapes and text in it. So is there an app which has drawing tools similar to Preview's annotation bar, i.e. it treats all drawn stuff as movable objects?