In the past few years, cryptographic currencies, also referred to as cryptocurrencies, gained much popularity. The first and most prominent cryptocurrency is Bitcoin, announced in 2008 by Satoshi Nakamoto. In the first quarter 2018, there have been more than 1,000 cryptocurrencies in existence. The common property of cryptocurrencies is that they are not owned or controlled by a single authority, e.g., by a central bank. In order to eliminate the need for a central entity, many cryptocurrencies use a blockchain for keeping track of payment transactions and state changes. The blockchain is a distributed ledger that is maintained by anonymous users connected via peer-to-peer networks. Besides keeping track of payment transactions and state changes, blockchains are applicable for a wide range of use cases. Popular use cases that came up in the last years are, e.g., digital voting, notary services, Supply Chain Management, auditing and control of ownership rights. The suitability of a particular blockchain for a given use case depends on various criteria, e.g., the costs for writing data into that blockchain, the time until a data record is permanently included and thus remains unchanged with high probability, the distribution of the network's hash power among miners or mining pools, the network's hash rate, etc. These properties can vary over the time. Thus, a particular blockchain can become unsuitable for a given use case over time. Such uncertainties can limit the practical value of blockchains. In order to overcome this limitation, we design and develop a framework that is capable of switching back and forth between blockchains. The framework monitors several blockchains, calculates their individual benefits and determines the most beneficial one. Furthermore, the framework is able to react to various events such as a rapid decrease of a network's hash power or a steadily increase of the costs for writing data into a blockchain. The assessment of several blockchains, the mechanism for reacting to various events and the switchover functionality enable users to switch to another, more beneficial blockchain in order to benefit from low costs, high performance or better security. The reference implementation of the proposed framework supports Bitcoin, Ethereum, Ethereum Classic and Expanse. The modular design of the framework allows future researchers to extend the framework, e.g., to add support for further blockchains.