Ingo Karkat has released ingo-library, which contains all of the common
autoload functions that he uses with his scripts. In his documentation he mentions previous initiatives for developing a Vim "standard library", which I think is an interesting idea.
Ingo has included a function for opening external instances of Vim, and functions for working with Vim error messages and warnings.
The Evil documentation is quite detailed, so jump in if you're not afraid to experiment with Emacs.