An efficient re-implementation of Electrum was recently developed by Roman Zeyde. It allows users to run an Electrum server on their machine with a required hardware not much more than a full node, it indexes the entire blockchain and the resulting index enables fast queries, this allows users to keep real time tracking of their wallets and transactions. As it uses the user’s machine, there is no need for the user to send requests to an external Electrum server preserving privacy for its users. It offers low CPU and memory usage, low index storage overhead and fast synchronization to the blockchain.
You can check out the implementation on Github from here.