A glass cutter is a small, specially designed hand tool, usually manual and used for cutting glass with both safety and precision. They're largely inexpensive and, depending on whether you're a hobby enthusiast or professional, you can choose something that's either entry level or up to an industrial standard.
If you already own a small power drill or rotary tool you're as well to purchase additional bits and tools that are specifically for glass cutting. If not, and you enjoy crafting at either a hobby or professional level, consider investing in one as they're a popular tool that many choose to use for cutting glass, tiles and so on.
One of the best secrets I know in relation to cutting glass is how well you score the glass, prior to the actual breaking of it. That and how patient you are, otherwise you'll never quite get the breaks that you're looking for. The five best glass cutters are featured below. Some are traditional hand tools, others are attachments. They're all popular, well rated and good value for money.