There are two companies building Ark

Ark Labs: docs.arkadeos.com

Second: docs.second.tech

There is trust involved to an extent in Ark, you need to trust that the Ark server won't collude with the sender of the payment to double spend it, but that's only for payments that you receive instantly, if you wait for some time your balance (called VTXOs) can be included as part of an aggregate txn that the Ark server makes after an interval which removes the trust assumption