K2 is a Windows Server platform that allows the creation and management of business workflows that consume data from a variety of data sources; on top of the .Net platform.
K2 is an enterprise BPM (business process management) platform written by SourceCode; that leverages and extends a variety of Microsoft technologies (.NET, Active Directory, SQL Server, SharePoint, Visual Studio, and Visio), and other technologies, such as SAP.
K2.net 2003
K2.net 2003 is, essentially, only a workflow designer, client and server. However, it does integrate with a few Microsoft technologies (for example Windows SharePoint Services). The user interacts with a flowchart and wizards in order to design the workflow process, in addition to being able to write custom .NET code.
K2 blackpearl (2007)
Blackpearl introduced the notion of SmartObjects, which are a abstract (extendable) representation of a data source. SmartObjects are one of the primary means of integration in the blackpearl line. For example, they are used to access SQL, SharePoint and SAP data.
In the first release, Visual Studio and Visio were used for the design/development experience. Subsequently an independent designer (K2 Studio), and a SharePoint integrated designer was released. The design experience is very similar to K2.net 2003, even though it was written from scratch.
Following the release of blackpearl, a 'slimmed-down' version called K2 blackpoint was released, the biggest exclusion being the ability to write custom code in workflow processes (as no Visual Studio integration is included).
K2 connect is a release of K2 that is geared primarily toward SmartObjects SAP integration.
K2 Five
K2 Five was released in November 2017 and most recently, K2 Five V5.3 was released in May 2019.
K2 Five brings a number of improvements and changes to the platform. K2 Studio is no longer supported. All development must now be done in the online Management and Designer tools.
One of the biggest changes is that new K2 workflows can no longer be developed using Visual Studio. Existing blackpearl (4.7) workflows still need to be amended using Visual Studio. To use the new online-only Workflow designer, you have to recreate these workflows.