I was trying to find a good alternative to the reporting features available in PostBook and came across BIRT (http://en.wikipedia.org/wiki/BIRT_Report). It is actually in JAVA but it will prove to be a good alternative to OpenRPT.
But unfortunately we cannot use it or integrate it directly in PostBook. I think this tool should be also integrated as an alternative to OpenRPT.
It also supports OLAP which is necessary in many a situations.
Just my 2 cents. ;)
Regards,
Yogi Yang