Virto Cross Site and Cascaded Look up is a powerful tool to use for SharePoint information, and for joint display of associated data from several distinct sources including lists and sites. The component quickly cross-references existing data from a list or site and then applies a combination of filters to reduce the number of options presented in the drop down menu of your look up field and eliminating the possibility for error as a result of incompatible values.
The component allows to:
Cross-site look up of a SharePoint list from current site collection
Build parent-child relationships between list columns so that the value you choose in the parent column determines the options presented in the child column
Set relationships between lookup fields
Add multiple selections for look up fields
Convert standard look up to Virto look up
Many other options for convenient SharePoint data displaying, grouping and filtering

As an example, we will do a case where you need to aggregate information from a list of clients which are grouped by countries and cities. We have created three look up fields with the dependence country -> city-> client. This means that when a user adds a new item to the list, he selects a country and a list of cities of the country will be displayed accordingly. And when the list of cities is defined, the same happens with clients list. Enter title of the look up and start typing a country name. The list of countries will be displayed. Click on the required country and use the arrow button to add this country to the look up. As you add countries to the look up, the list of cities will change accordingly. And as you select cities, the list of clients will change as well.