Is there an equivalent of view modes for form editing? I have a content type with a lot of fields. End users need to create content of this type, so I want to provide them with a simplified form so that they can create a content item and edit it without knowing about the majority of the options. Then those who want to dive into the complexity could have an advanced form which exposes them.

View modes looked like the kind of thing I'm trying to do, so I used hook_entity_info_alter to create a custom view mode and started trying to figure out how to control the view mode used by node/add/my-content-type. After digging into the code I've realised that view modes are used by node_view and that adding or editing a content item uses drupal_get_form instead.

Is there some "form mode" which allows different field type and grouping configuration for different "views" onto a form?
1 - Panels/Page Manager
If you're using Panels and Page Manager (part of Chaos Tools) then you can break up the node/add form by enabling/overriding the node_edit page manager handler and creating a Panels layout to show the individual fields.
Just set a variant to only react on creation of your particular content type, and then arrange the form fields as you wish. This will let you split out any form fields, as well as provide a General form pane that will add any fields that you've missed out.
IMPORTANT NOTE COURTESY OF LETHARION
Something I didn't realise due to the fact that I always put the general form on the page, is that if you DON'T output ALL fields, then &quot;form api will interpret it as &quot;the user deleted the content of those fields&quot; and will send back empty values. This could result in the loss of existing data, so be careful.

2 - Solely Fields/Field contrib
You could also try Field Permissions if the form is permissions based, or use a Field group with some collapsed fieldsets or tabs etc to initially hide the fields if they are not permission based.