Aquiline tracking is from a carrier called Aquiline who is a third party carrier who picks up the package and then eventually transfers and hands off the package to USPS, UPS, FedEx, DHL etc.
Aquiline tracking and packages are delivered by USPS.
When I've ordered something through eBay and it was sent out by Aquiline tracking it was delivered by USPS to my address.
Aquiline picked the package up from the seller and took it to the closest USPS hub and then USPS did the final delivery.
Aquiline tracking can also sometimes be delivered by UPS, DHL and FedEx.