sorry , currently there is no document about these activitese , these activites have not been tested completed .
Here I can give you a description:
1)EnableStepModification --- you may be know Modification is an important function of sharepoint workflow , by add EnableStepModification , you can enable
the workflow be forced managed Step by administrator (Like goto any step) . But this activity should need a Modification page to help to complete this function.
2)Rounter is a good activity , and It can be used in Step activity , just like Decision activity , it can control the next step of the workflow.
Rounter has a AddBranch Menu to add many Rule Activity , Rule activity has a Condition property and a Target property , when the Condition is true , the workflow will goto the activity named by Target property.
The difference between Rounter and Decision is that Decision only have two branch , the Rounter and Rule can have many branch.
Step + Task(Or MulitiTask or GroupTask or any other activity) +Rounter and Rule can provide more complicated function.
3) ToOriginator , is a very simple activity , It assign a Task to a workflow Originator. It just inherit from Task activity and Provide the workflow Originator as the workflow user.
4)MoreApprove is a very complicated activity , Here I will don't descript it.
5)RoleTask , you can find a RuleDefinitions property of the workflow class , by RuleDefinitions you can define some role and it's user in the workflow level ,
and by RoleTask , you can assign workflow tasks to the users in a role .