Double donations or maybe multiply donations by X up to X amount. We get donors who commit to match every donation up to X dollars, so basically every donation would be doubled on the campaign thermometer until the match was met. Would want to be able to add multiple matching donors/sponsors to a campaign. We've never done this, but the idea with it being Multiply vs Double is maybe a donor would commit to triple a donation (or a different multiple) up to X amount.
Would want to have the matching donors featured on the campaign page and fundraising pages along with their own thermometer of how much of their match had been used and how much is left.