Someone owes me money, or I lent money out. Is that zakatable?

It depends on the kind of debt. Money you lent, and payments owed to you from selling trade goods, are zakatable every year while they are outstanding. You can pay on them each year, or wait and pay for all the years at once when the money comes back to you. Softer claims, such as unpaid salary, an inheritance you have not received yet, or a settlement, are not counted until the money is actually in your hands.