It would be a nice new feature if workrave could track what I do between every 
rest break.

I work from home a lot and use workrave to measure the length of my workday as 
well as using it to remind me to take breaks. At the same time I have to 
product reports of the amount of time I've spent on tasks. I keep track of 
this separately but it would be nice if, whenever workrave starts a rest 
break, it could give me the opportunity to enter a sentence describing what 
I've just been doing. It could then list everything I've done in a week in the 
stats.

I know this isn't really within the central remit but I thought I'd suggest it 
and see what you think.

Workrave is an RSI tool, and I do not think we should include activity tracking.
If we did, the end result would probably be a poor time/activity tracker at
best, since it will always be a bit of a kludge bolted on top of a program that
was not meant for that goal. 

A better option if you really depend on any such feature is for Workrave to
cooperate with an existing time/activity tracker. Meaning, Workrave's break
window could include an option to select your current activity, but it only
passes this on to a 3rd party program. That way, stuff like report generating
and all other things that should be included in a proper time tracking tool need
not be included into Workrave.

But I really doubt that with typical use case scenarios Workrave's breaks
coincide with the user starting a new activity.