Found via FlightScout, useful for seeing the range of cheaper dates, although the prices actually seem lower when you click through to skyscanner (the joys of caching I guess).
Example:
15 July to 2 Sep
From: Sydney
To: BERLIN, Germany
Airline: Scoot
Stopover: SIN (Singapore)
Yes, it's a budget airline. But if you can travel with just carry-on (and many of us do!), and put up with the quality of Scoot's inflight service, then for this price you're in Germany for 3 months (in example at least).
Should come with tips what to do in Singapore starting from 4am during 21h stop over