The web3 connector is still early alpha - DO NOT USE IN PRODUCTION. 
datasources.json :
...
"ethereum": {
"name": "ethereum",
"connector": "web3",
"url":<optional>
},
...
If you do NOT specify a RPC URL, the connector will assume "http://localhost:8545". Don't want to run your own node? Check out Infura!
Now just create a model that represents your Solidity based smart contract, for example
{
"name": "Contract",
"plural": "contracts",
"base": "Model",
"idInjection": true,
"options": {
"validateUpsert": true
},
"properties": {},
"validations": [],
"relations": {},
"acls": [],
"methods": {},
"ethereum":{
"contract":{
"sol": "server/SimpleStorage.sol",
"name":"SimpleStorage"
},
"gas": 3000000
}
}
where "SimpleStorage" (above) is the name of the constructor for the smart contract. The connector will compile the contract and doing a POST at the model base route will deploy the contract and return the contract address.
For an example to get you up and running, checkout the web3 demo.
- Tic-Tac-Toe
- Vidbit (private beta, tweet me to get on the list @jamesyoung)
If you are building a decentralized application using the web3 connector, tweet me : @jamesyoung and I'll add you to the list of dapps.