The shape kit: shapes that carry meaning
Pick a step by what it means, not by what it looks like. Decisions are diamonds, datastores are cylinders — always.
Meaning first
In o-flow you choose "Decision" or "Database" from the palette, and the right shape is drawn for you. You can never accidentally use a diamond for a process step, because the diamond is the decision.
A small, deliberate set
Terminator, process, decision, input/output, document, database, subprocess, connector — plus a borderless free-text label. That is enough to express almost any technical flow, and few enough that diagrams stay readable.
Restyle freely, re-mean never
You can change a shape's colour and size as much as you like; its meaning is fixed. Cosmetics and semantics are kept separate on purpose.