Q:

In Vim is there more than one way to leave insert mode?

There are several commands that do something and then enter insert mode. Are there also commands that leave insert mode and do things?
For example, I frequently do this...
control[ : w return
Before I create a mapping, is there already Vim command that does that?

A:

In addition to Esc (which is identical to ^[), ^C also exits insert mode.

A:

The only one I can think of is c-o, which lets you run one command in normal mode then drops you back into insert mode.
For example, a<c-o>~b would result in Ab.

A:

If you'd like to map a few keys to do things like save a file while in insert mode, you can use the imap command.  This binds F2 to exit insert mode and save the file:
:imap <F2> <Esc>:w<CR>

This binds F2 to exit insert mode, save the file, and re-enter insert mode:
:imap <F2> <Esc>:w<CR>a

Or:
:imap <F2> <C-o>:w<CR>

