Gravity coin built on top of block chains using cryptography, therefore exchange of coins takes place directly between a seller and a buyer—with no third party. There is also no central server (except for DNS seed which you may need the first time you run Gravity coin), Gravity coin runs on its own anonymous P2P overlay.
In Gravity decentralized network distributed system (As a P2P network) there are usually trade-offs to be done in terms of efficiency, security, scalability, robustness and decentralization. In terms of scalability, decentralized approaches have a bigger potential.
Gravity coin P2P network is a distributed network, a large scale network, without any centralized service. Nevertheless, some services which are supposed to be decentralized in a P2P network, may need a centralize server (or a set of servers). This is for example the case for the JOIN procedure where a new node enters the network. Joining the network usually requires to know a node that is already a member of the P2P network. The use of a set of servers is a feasible solution to maintain a sufficient list a node that are already in the network.