.blend is a file format used by the open-source 3D application Blender. It can be used to store several different scenes all in one file, and extra files such as sound effects and image textures can also be included. Files saved in the .blend format are almost completely forward and backwards compatible, and cross-platform compatible, with other versions of Blender.
The first 16 bytes of a .blend file from Blender version 2.44 are these (ASCII):
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