Attassa specializes in turning Microsoft's Outlook e-mail software into a file collaboration hub, while Zosh makes editing and signing documents on the iPhone extremely easy.
With these purchases, YouSendIt appears to be anxious to merge file-sharing, e-mail collaboration and e-signatures into a single service with enterprise appeal and build out a more robust (likely for-charge) experience for its 15 million registered users.
It's unclear how the individual services' existing users will be affected by today's news. Both services' websites have been taken over by YouSendIt and feature the acquisition announcement prominently. As of right now, Zosh's iPhone application [iTunes link] is still available for download in the App Store but the application appears to be a bit unresponsive.
To date, YouSendIt has raised more than $50 million in funding. In August, the veteran startup closed a $15 million Series D round led by Adams Street Partners. Those funds were likely applied to the acquisitions of Attassa and Zosh.