The launch of the Google Apps Marketplace  means GOOG's giving every Web service the same privilege Buzz had: integration with Gmail, Docs, Calendar and the rest of the GApps gang. If you administer a Google Apps account for your business, family, or softball team, there are four applications that are worth installing right now.
What You'll Need
In order to install apps in the Google Apps Marketplace, you'll need to be an administrator on a Google Apps  account. Setting up a Google Apps account isn't difficult, but it requires both a domain name and some elbow grease. The Apps Marketplace doesn't work with vanilla Google accounts (your email@example.com email address).
To install an app, first find it in the Google Apps Marketplace , then click on the "Add it now" button. Enter the domain name associated with your Google Apps account. Log into your administrator account, and GApps will walk you through a three-step process for getting the new app set up. Once that's done, it will appear in the "More" drop-down at the top of your Gmail, Google Docs, and Calendar accounts, as shown in the screenshot above, for every user on your domain.
Got it? Now, here are four apps worth trying. Click on the title to install them.
The underdog in Web-based office suites, Zoho , makes several products that directly compete with Google Docs--but a few that also fill in GApps' gaping holes. For example, Zoho Projects is a Web-based project manager that's worth taking a look at for your GApps workgroup.
What you get: Access to your Google Docs inside Zoho, and the ability to show project deadlines on your Google Calendar, plus easy account creation for everyone in your Google Apps workgroup. Zoho Projects is free for one project, pricing starts at $12/month.
Alternative: Manymoon  is a free alternative with a more social bent, with Twitter-like status updates and similar Google Docs, Calendar, and Contacts integration.
Aviary Design Suite  Image and Sound Editor
Aviary  is a powerful Web-based image and audio editor that helps you add effects to and tweak images, create logos, business cards, labels, vector graphics as well as edit audio files like podcasts. This is a must-have for anyone who wants to edit images for inclusion in a document or slideshow in Google Docs.
What you get: Aviary for GApps automatically saves the files you create to your Google Docs account, in a folder it creates automatically called "Aviary."
When you want to work in Microsoft Word on your desktop but save all your files in the cloud for anywhere-access, you need a good syncing tool, like OffiSync. The toolbar for Microsoft Office uploads your work on the desktop to Google Docs or Google Sites every time you save it, seamlessly.
What you get: OffiSync spares you the hassle of manually uploading files to Google Docs every time they change. Unilike the other apps listed here, OffiSync is a Windows download that adds a toolbar to Microsoft Office. Using it, you can set group access permissions to the document, and browse your Google Docs and Google Sites folders to choose where to save your document online, as well as search Google
Alternative: Google's recent acquisiton, DocVerse , offers very similar functionality.
TripIt Travel Plans  Sharing and Coordinating
One of the most useful travel planning Webapps out there, TripIt , now lets you see who in your GApps workgroup is going where when. Using TripIt is simple: when you book travel online and get an email of your itinerary from the airline, you forward that email to firstname.lastname@example.org. TripIt automatically parses out your trip's details, and builds an itinerary page with useful information about the weather, local time, directions, online check-in, and travel delays, which you can share with your friends, family, and co-workers.
What you get: With TripIt in Google Apps, you can automatically notify everyone in your company (and only people in your company) of your travel plans, and integrate them into your Google Calendar. You can also see who's traveling where on a company travel map.
The biggest benefit to using these apps in Google Apps boils down to three things: the ability to skip the separate site registration process, automatically sharing information with other users in your domain, and easy hooks to Google Docs, Calendar, and Gmail. While Google Apps users don't get all the services of a vanilla Google account--like Voice, Reader, and Wave--the new Marketplace makes a GApps account a whole lot more desirable for enterprise users.