From what I know GridCoin is not a market for purchase-sale of the computing power.
GridCoin computes only for white-listed projects, while our project will be available for anyone. We also base payments on smart-contracts system and on Ethereum blockchain.
The closest projects to us are iex.ec (they use own middleware similar to ours) and Golem. Competitors are cloud computing companies, including Amazon GPU clouds etc.
GridCoin uses projects with external servers, which are using BOINC servers and then are just rewarded by GridCoin. We are going to build our own decentralized servers network, where servers will be supernodes distributing tasks to miners nodes and validating them. We just use BOINC code as a starting platform. Any trusted node (combined PoS+PoW) can become supernode-server.
Then it is also expected that there will be machine learning algorithm, optimizing applications/hardware and automatically selecting hardware for certain applications and vice versa thus increasing miners efficiency.