Previously, you may have used tools like dd or similar to write images to disk. These tools, while they've worked fine for many people for a very long time, were often cumbersome. Images may be compressed and require you to decompress them. Some storage devices may appear on your system right alongside the disks you use for your OS, photos, or general storage. With low level tools there is a risk of accidentally writing to the incorrect disk! At the end of the process most users rarely performed any check and may have been booting devices from incomplete writes on faulty storage.
Etcher alleviates all of the annoyances to writing to storage by providing a beautiful GUI that helps a user select the image and disk quickly. After the write is complete a checksum is performed automatically to ensure the image was written correctly.
Etcher can be used to write images to SD cards for the Raspberry Pi or BeagleBone devices. It can also be used to write ISO images of your favorite Linux distribution to quickly create a bootable USB disk. Elias over at thing-printer, creator of the Replicape 3D printer controller, has been suggesting it in tutorials for getting started with the Replicape 3D printer controller. After using it a few times ourselves, the team over here at TamarinTech will also be suggesting that users get familiar with Etcher for their projects.
Even proficient users of xzcat and dd can appreciate the ease and reliability provided. Etcher is free and open source software.