The terms of the deal were not disclosed. Manymoon said it will operate as a separate unit and will continue to offer its free and premium products to clients. It also plans on developing new features. Manymoon said Salesforce will help it grow by assisting with scalability, security, performance and support. In addition to the Google Apps platform, Manymoon is available through LinkedIn and the Chrome Web App Store. Manymoon said it has 50,000 businesses using its software with 1,000 signing up each week.

The Manymoon pick-up underscores Salesforce’s emphasis on social collaboration. The company on Monday launched Chatter.com, its Facebook-like enterprise social platform. It also invested $4 million today in Seesmic, which develops applications that monitor social networks across mobile devices.

Marc Benioff, CEO and founder of Salesforce, recently spoke at the GigaOM Net:Work conference talking about the power of social tools in enterprise, which he said have the ability to flatten hierarchies and democratize companies. The move to social is part of a larger push toward Benioff’s vision of Cloud 2, which he said encompasses cloud computing, social networking and mobile. With all the talk around social, Benioff is showing this week that he’s putting his money where his mouth is.

Related content from GigaOM Pro (sub. req.):

• Enabling the Web Work Revolution
• Report: The Real-Time Enterprise
• Who Owns Your Data in the Cloud?

Manymoon is well-designed, with a clean interface throughout. Of course, that’s true of a lot of project management web apps, and especially the free ones targeted at the independent, rather than the enterprise, user. Commands and tools are housed in submenus and tabs to keep visual clutter on any given page to a minimum. And I do find that everything is located where I intuitively expect it to be, which is not necessarily always the case in other apps.

Your home screen looks more like a Facebook newsfeed than the dashboard-type interface you might be used to from other comparable services. You receive updates here based on the recent activities of members of your project team. Things like the creation or completion of a task or a project, what any member is currently working on, and additions to the project team will all show up here as they occur.

Setting up a project is easy, and assigning sub-tasks within that project is as complicated or as simple as you need it to be. By default, task addition is shown in a convenient quick entry mode: all you need to enter is a title. Clicking “Show options” allows you to add more detailed information, like a due date, priority, project staff responsible and file attachments.

One really nice feature that sets Manymoon apart from other similar services is its Google Apps integration. You can tie your project and task deadlines to Google Calendar, right from within the web app, automatically. And you can attach documents directly from your Google Docs account, as well as those you upload from your hard drive. It’s definitely a huge plus if you depend on Google Docs as much as I do.

They’ve taken some cues from Facebook and Twitter, in that you can quickly and easily post about what you’re currently working on, or a useful link, from entry fields on the right of the home page. This certainly comes in handy when you want to draw your team’s attention to a useful resource without going to the trouble of sending a mass email.

While the basic version is free, Manymoon also offers two levels of upgrade, which offer you more storage space, and other custom options, for $5 and $10 a month. Since, for my purposes the 5MB allowed on the free version is more than enough, I highly recommend Manymoon as an inexpensive project management solution, especially to those who already depend heavily on Google Apps.

Does the Google Apps integration in Manymoon appeal to you?

Related research and analysis from GigaOM Pro:
Subscriber content. Sign up for a free trial.

• Why iPad 2 Will Lead Consumers Into the Post-PC Era
• The Near-Term Evolution of Social Commerce
• Content Farms: The Players, The Benefits, The Risks