If you're looking for something other than QuantConnect, there are several other platforms for building, backtesting and executing algorithmic trading strategies.
AlgoBulls is a full-featured platform for building, executing and monitoring sophisticated trading strategies. It supports trading on multiple exchanges and brokers, has a library of pretested strategies, and offers backtesting and live trading through an interface that's easy to use. The service is geared for people of all skill levels, with flexible pricing.
Another contender is Tradetron, a multi-asset, multi-currency and multi-exchange service. It offers a web-based strategy builder, backtesting engine, social trading and detailed performance reports. Tradetron lets you turn your trading ideas into a business and tap into a marketplace of tested strategies, so it's good for algorithmic trading.
And if you're into cryptocurrency trading, CryptoQuant offers a powerful on-chain and market analytics service. It offers access to a broad range of on-chain and off-chain data, proprietary metrics and customizable analytics tools. You can create your own metrics, build your own dashboards and tap into community-created indicators, so it's good for institutional investors and professional traders.