Lay out the steps of a procedure, a decision with its answers, a data pipeline or a reaction work-up as blocks: rectangles, terminals, decisions, inputs and outputs, databases, documents and subprocesses, each holding its own text.
Join them with straight, elbow or curved arrows that ride on the blocks and follow them when they move, with a head at either end and a label on the line. Type a diagram as text — Start -> Weigh -> Dissolve — and it is laid out for you; save it as SVG or PNG, or paste it into draw and write.
Draw blocks, join them with arrows that follow them, or type the diagram as text, then save it as SVG or PNG. The tool needs JavaScript, because the diagram is drawn in your browser.