One of the ways that the open-source/crowdsourcing idea could be used to create greater government transparency would be to include the federal budget. The basic page would show the CBO or OMB projections for revenue/expenses and allow the user to adjust future economic growth/inflation/healthcare inflation to see what it would do to the federal budget deficit/surplus.
The next addition would be to include federal taxation into the equation to allow the user to see the impact of changes to federal taxation to the overall budget picture.
The final phase would be to include every item of spending currently in the budget and show the impact of expanding/reducing/eliminating any given program. Users could make their changes and then submit the modified budget. The data from these submissions could then be aggregated to see what programs have the most support for expanding or reducing and this could be then used as another metric to view the public support for different programs.