1) Guide the customer through creating professional-grade invites. That part is relatively straightforward.
2) Print and mail the invites
3) Provide an RSVP service available to the couple and their vendors -- the caterer needs to know who wants vegan food but, honestly, the bride and groom don't care.
Finally, if you REALLY want to provide something disruptive: take a handwriting sample from the bride and/or groom, turn it into a font, and produce the thank-you notes (they need to look hand-written). I have no idea how you would do this, but having been through a wedding myself I remember utterly loathing this part.