The theory behind open-source software is that it avoids many of the pitfalls - including cost - of closed alternatives. But Steven Buckley, who runs Christian Aid's common knowledge programme, prefers to buy software from the likes of Microsoft. Is this not odd for a charity? "Open-source doesn't mean free," he told BBC World Service's Digital Planet programme. "Quite often, if you install open-source software within an organisation, you have a support contract that goes with it - it's an essential part of operating that software. Over time, that can actually cost more than having Windows on an enterprise machine."