Podio

Podio is a cloud-based collaboration platform which was founded in 2009, and subsequently taken over by Citrix in 2012.Businesses can use it to create customized applications with little-to-no technical knowledge. The Podio App Market offers hundreds of free applications such as product, sales and project management. There are apps for customer relationship management and applicant tracking.
You can sign up for Podio here
Users can create and build their own apps, plus Podio has its own apps for