First of, I think you can continue to use lshistory and adding a
"%[activity]p" to the format string.

On the recent changes screen i want:

• instead of "<number> <userid with link> <details link>" I would
  like something like "<number> <Activity name/headaline> by <userid
  with link> <maybe number of files> <details link>"
• Only show each activity once even when multiple files in a activity changed

On the changes in a build screen:

• Grouping by activity instead of checkin ?!
• in the box where you currently write the comment, put the activity name
• List the files as normal expect for when there is a comment, then
  show that along with the file
• Perhaps parse and cleanup the file string e.g. transform
  "vobs/projects/Usi_Server/sample-application-ejb/.settings/org.eclipse.jdt.core.prefs@/main/Usi_Release_2_1_int/1

• create version" into " Created version 1 of
  vobs/projects/Usi_Server/sample-application-ejb/.settings/org.eclipse.jdt.core.prefs
  in stream Usi_Release_2_1_int"

• If the activity is a deliver or rebase (name starts with deliver. or
  rebase.) then run a lsactivity with "[contrib_acts]" in order to get
  the contributing activities. The list of contributing activities
  should be shown above the files list.

The full block for a activity in the changelog will be.
"
<begin header box>
<userid> on <date>
<activity headline>
– Description: <acticity description if any>
</end header box>
Contributing activities:
<First contributing Activity headline>
<Second contributing Activity headline>
Files involved:
<version> of <file path>
– <comment if any>
<version> of <file path>
– <comment if any>
"