From the September 2010 issue of Entrepreneur

It's Google's world--the rest of us just work in it. Beyond the digital services giant's increasingly ubiquitous search, mapping and advertising solutions, it also has emerged as a leader in cloud computing: More than 2 million businesses have adopted the Google Apps suite, which promises firms a cost-efficient and hassle-free alternative to Microsoft Exchange or Lotus Notes.

Growing demand for enterprise software outside of Google's fields of expertise prompted the March introduction of Google Apps Marketplace, an online storefront aggregating cloud applications from more than 50 third-party allies. Given the volume and breadth of applications available, comparison shopping in Google Apps Marketplace can be challenging. Here are some must-have apps for small businesses.

BatchBook Social CRMBatchBook Social CRM Organize contacts, view customers' social networking activities and track leads all in one place with BatchBook Social CRM, a customizable, web-based contact relationship manager that synchronizes with existing Google contacts to more effectively keep tabs on all of your business relationships. Prices start at $9.95 per month.

OffiSyncOffiSync This Microsoft Office 2003, 2007 and 2010 add-in extends core Word, Excel and PowerPoint functions via collaboration capabilities powered by Google Docs and Google Sites. With the free OffiSync application, users can maintain the familiarity and comfort of Office while leveraging Google-based web solutions.

Rhino AccountingRhino Accounting A free alternative to QuickBooks Online, Rhino Accounting offers small businesses an easy-to-use solution to their basic bookkeeping needs. Users can see their reports in Google Docs and send invoices via Gmail; they can also access their financial data at home or on the road from any web-connected device. Rhino backs up data daily, weekly and monthly across multiple locations and employs bank-level 256-bit SSL encryption to guarantee data security.

Tungle.meTungle.me Simplify and streamline your day with Tungle.me, a free personal scheduling application that lets entrepreneurs publish their availability to colleagues and customers alike. Tungle.me integrates with Google Calendars to span schedules companywide, making it easier for clients to schedule meetings while eliminating double bookings, time zone confusion and other snafus.

TripIt TravelingTripIt Traveling to meet with clients, collaborate with partners or attend a trade show? Forward your booking confirmation details to plans@tripit.com and the free TripIt app organizes and shares your itinerary with family, colleagues and even social networking contacts, making it easier to coordinate schedules. Itineraries can be customized to include weather, maps and directions and can be accessed via iPhone, Android and BlackBerry devices.