A great platform to
QuantConnect is a great platform for retail quants and quant firms, which do not want or do not have the resources to build the whole backtesting and live trading infrastructure and do all the data wrangling themselves.
It provides an easy-to-use backtesting platform for your strategies, and without modifications of the code, they could be deployed for live trading. Most importantly, it has all the data you could wish for cleaned up and ready to use.
I would like to add that you can really run a great variety of strategies, on single etf/futures/crypto, to universes of stocks and from technical analysis to calendar effects and using third party data (e.g., sentiment), etc. Also you can use usual Python Machine Learning packages, etc. So far, I haven't come across a strategy that I could not somehow implement within the QuantConnect ecosystem.
For me, this is as straightforward as it gets, so I can wholeheartedly recommend.