Currently we are using jasper plugin to modify the dashboard data to provide report in desired output, which requires additional java coding effort.
We are in search of any open source tool integrated with dynatrace which reduces the coding effort
Depending on the type of dashboard the User Session Export might also be an option.
You can push the data to elasticsearch and build dashboards with kibana for example.
For timeseries metrics you would need to get the metrics via API as Sebastian mentioned.