Other than governmental employers, who can establish a 457(b) plan?

The organization must be a tax-exempt organization under IRC 501(c), excluding churches as defined under IRC 3121(w).  The most common example of a non-governmental organization sponsoring a 457(b) plan would be a charity which is tax-exempt under IRC 501(c)(3).  Other examples include certain credit unions, country clubs, civic leagues and other groups organized under IRC 501(c).