Excel Services extends the Excel desktop experience to the Web and is built upon a server-hosted version of the Excel calculation engine. Advantages include enabling users to interact with Excel workbooks directly in their web browser, without having to have the Excel client installed on a client computer. This increases the overall reach and use-case scenarios of Excel-based data and applications.


Microsoft Office Web Apps includes an online companion to Excel that enables users to access and edit documents, regardless of their location. The Excel Web App is also available to users through Windows Live and to business customers with Microsoft Office 2010 volume licensing and document management solutions based on Microsoft SharePoint 2010 Products.


The following table provided by Microsoft SharePoint Insights
 lets you see shared and exclusive features for Excel Services and the Excel Web App.

Capability

Excel Web App (part of Office Web Apps)

Excel Services in SharePoint 2010

View

x

x

Edit

x

Collaboration

x

Create New

x

Create Excel-Driven Dashboards

x

Display New Visualization

x

x

External Data

x

x

- Anonymous

x

x

- Secure Store

x

- PowerPivot

x

Web Services API

x

REST API

x

JavaScript OM

x

User-Defined Function

x

x

 
See the following TechNet articles for more information: