This is a generic & customizable lookup component built using Salesforce Lightning and SLDS style.
It does not rely on third party libraries and you have full control over its datasource.

Features

The Lightning Lookup component provides the following features:

• customizable data source that can return mixed sObject types
• single or multiple selection mode
• client-side caching & request throttling
• built-in server request rate limit mechanism

The Lookup Lightning component is documented using Aura documentation.
You can access it from this URL (replace the domain):
https://<YOUR_DOMAIN>.lightning.force.com/auradocs/reference.app#reference?descriptor=c:Lookup&defType=component

Prior to using the Lookup component, it is your responsibility to implement an Apex @AuraEnabled method (SampleLookupController.search in our samples) that returns the search results as a List<LookupSearchResult>. The method name can be different but it needs to match this signature:

@AuraEnabled
public static List<LookupSearchResult> search(String searchTerm, List<String> selectedIds) {}

The Lookup component exposes an onSearch component event that is fired when a search needs to be performed on the server-side. The parent component that contains the lookup must handle the onSearch event:

<c:Lookup aura:id="lookup" selection="{!v.selection}" onSearch="{!c.lookupSearch}" label="Search"/>

The event handler should do the following:

lookupSearch : function(component, event, helper) {
    // Get the Apex server-side action associated with this search (`search` in our samples)
    const serverSearchAction = component.get('c.search');
    // Passes the action to the Lookup component by calling the `search` aura method
    component.find('lookup').search(serverSearchAction);
}

Deploy the sample application with Salesforce DX by clicking on this button:

The default installation installs the Lookup component and a sample application available under this URL (replace the domain):
https://<YOUR_DOMAIN>.lightning.force.com/c/SampleLookupApp.app

If you wish to install the project without the sample application, edit sfdx-project.json and remove the src-sample path.