I started in on a story at work where I needed to add some reports on one of our internal applications. In the past, I have just done some query and then iterated over it in the view, creating a report manually, but it seemed that I was always doing the same sorts of operations and that there should be some tool that makes that all easier. So, I started searching for reporting tools in ruby, googling and asking friends and the only thing I found was Ruport.
It seemed pretty cool and I was really impressed with the demos and my first few passes, but after a half day of struggling, I just could not force out of it the reports I was looking for. It did grouping weirdly, I didn't seem to have easy control over the rendering of the html, I couldn't highlight cells, the pivoting functionality was destructive to other row data and you couldn't change more than one column in a single pass.
My biggest problem was that the data manipulation and the report formatting was so tightly coupled. It was an interesting api, so I considered hacking on it, but it didn't seem too complex and I wanted the architecture to have a cleaner separation of what I feel are the three major steps of reporting - data manipulation, report formatting and output rendering. So, I decided to start my own project and a day and a half later, I had Munger, the alternative ruby reporting library.
The library is about two days old, but it's pretty usable already. If you'd like to help out, fork and hack!
Simple Example

Here is a simple example.

result = AdAirings.find(:all)
report = Munger::Report.from_data(result).process
puts Munger::Render.to_text(report)

will result in :

|airtime | airdate    | clicks | advert | 
------------------------------------------
|15      | 2008-01-01 | 301    | spot 1 | 
|30      | 2008-01-02 | 199    | spot 1 | 
|30      | 2008-01-03 | 234    | spot 1 | 
|15      | 2008-01-04 | 342    | spot 1 | 
|30      | 2008-01-01 | 172    | spot 2 | 
|15      | 2008-01-02 | 217    | spot 2 | 
|90      | 2008-01-03 | 1023   | spot 2 | 
|30      | 2008-01-04 | 321    | spot 2 | 
|60      | 2008-01-01 | 512    | spot 3 | 
|30      | 2008-01-02 | 813    | spot 3 | 
|15      | 2008-01-03 | 333    | spot 3 |

A Simple Pivot

result = AdAirings.find(:all)
data = Munger::Data.load_data(result)

new_columns = data.pivot('airdate', 'advert', 'clicks')

report = Munger::Report.from_data(data).columns([:advert] + new_columns.sort).process
puts Munger::Render.to_text(report)

becomes:

|advert | 2008-01-01 | 2008-01-02 | 2008-01-03 | 2008-01-04 | 
--------------------------------------------------------------
|Spot 1 | 301        | 199        | 234        | 342        | 
|Spot 2 | 172        | 217        | 1023       | 321        | 
|Spot 3 | 512        | 813        | 333        |            | 

A More Complex Example

result = AdAirings.find(:all)

data = Munger::Data.load_data(result)
data.add_columns([:advert, :rate]) do |row| 
  rate = (row.clicks / row.airtime)
  [row.advert.capitalize, rate]
end

report = Munger::Report.from_data(data)
report.sort('airtime').subgroup('airtime')
report.aggregate(Proc.new {|arr| arr.inject(0) {|total, i| i * i + (total - 30) }} => :airtime, 
                        :sum => :rate)

puts Munger::Render.to_text(report)

gives us :

|Spot   | Rate | Air Date   | Airtime | 
----------------------------------------
|Spot 2 | 14   | 2008-01-02 | 15      | 
|Spot 1 | 20   | 2008-01-01 | 15      | 
|Spot 3 | 22   | 2008-01-03 | 15      | 
|Spot 1 | 22   | 2008-01-04 | 15      | 
|       | 78   |            | 780     | 
|Spot 2 | 5    | 2008-01-01 | 30      | 
|Spot 1 | 6    | 2008-01-02 | 30      | 
|Spot 1 | 7    | 2008-01-03 | 30      | 
|Spot 2 | 10   | 2008-01-04 | 30      | 
|Spot 3 | 27   | 2008-01-02 | 30      | 
|       | 55   |            | 4350    | 
|Spot 3 | 8    | 2008-01-01 | 60      | 
|       | 8    |            | 3570    | 
|Spot 2 | 11   | 2008-01-03 | 90      | 
|       | 11   |            | 8070    | 
|       | 152  |            | 16770   | 

Wrapping Up
There is also cool cell and row styling, html rendering, etc, so check it out.