Complex sentence: Their first "real" campaign was the pledge they created for the Mephisto project by Rick Olson and Justin Palmer, that was used as a test-drive for Pledgie, although the Mephisto project already had a PayPal donation button.
Split into simpler sentences: Their first "real" campaign was the pledge they created for the Mephisto project. The pledge was used as a test-drive for Pledgie, although the Mephisto project already had a PayPal donation button.