OpenEthereum supports a dev mode that is particularly useful for Dapp development and demos. Thanks to its Instant seal consensus engine, transactions are “mined” instantly. No need to wait for the next block.
Run a development chain using:
openethereum --config dev
The created chain is initialized with an address that contains a lot of Ether - 0x00a329c0648769a73afac7f9381e08fb43dbea72. Its private key is 0x4d5db4107d237df6a3d58ee5f70ae63d73d7658d4026f2eefd2f204c81682cb7.
The default configuration should work fine in most cases. However, it can be customised. You can see the chain specification for the dev network in the source repository. You can make a copy locally, modify it and pass it to the --chain option. The last section of the file under accounts can be modified to add more accounts with lots of Ether. See the Chain specification documentation for more details.
To make multiple transactions confirm at the same time use --reseal-min-period 0 and to make transactions free use --gasprice 0.