Expert Advisors (EAs) are programs that can be used to automate trading and can be written using the MQL4 language or purchased from a third party. Keep in mind that EAs run locally on your computer and will not execute strategies when disconnected from the server. For qualified clients, EA hosting services are available to run your strategy on a secure VPS environment.
Please note that MetaTrader 4 allows you to run more than one Expert Advisor simultaneously. However, you cannot run more than one EA per chart.