Nerdtree
The NERD tree allows you to explore your filesystem and to open files and
directories. It presents the filesystem to you in the form of a tree which you
manipulate with the keyboard and/or mouse. It also allows you to perform
simple filesystem operations.
The tree can be toggled easily with :NERDTreeToggle which can be mapped to a more suitable key. The keyboard shortcuts in the NERD tree are also easy and intuitive.
Edit: Added synopsis