Coming from Cinema 4D I was surprised that Blender does not offer the possibility to open multiple files at the same time. 

My workflow is based on using elements - be it parts, colors, textures, light setups - from previous models or colleagues. Or simply looking up how big, in which color, or where certain parts of the scene were created. Working with only one file opened seemed extremely limiting to me.

Adding other elements via Append seemed as cumbersome to me as closing the current model, opening an older one, copying the desired parts, closing the older one again, opening the current one again, and inserting the parts. (This is already awkward when described textually, but becomes a real work stopper when dealing with complex models containing many elements.)

Fortunately, Blender offers the possibility to open multiple instances if you have enough memory. But even this is only possible in a tedious way via terminal or with tricks.

Multi Instance for Blender is the convenient alternative for all platforms* to open another Blender instance quite easily via the menu.

* works on Linux distros with gnome terminal only

M.I.B. works on all platforms and makes working with multiple files a breeze.