OWIN is not a framework. OWIN is a specification on how web servers and web applications should be built in order to decouple one from another and allow movement of ASP.NET applications to environments where at the current state it is not possible.
Prior to OWIN, when you are building ASP.NET application, you are inheritedly bound to IIS due to the heavy dependency on System.Web assembly.
System.Web is something that exist ever since ASP (non .NET version) and internally contains many things that you might not even need (such as Web Forms or URL Authorization), which by the default run on every request, thus consuming the resources and making ASP.NET applications in general lot slower than it's counterparts at i.e. Node.js.
So OWIN itself does not have any tools, libraries or anything else. It is just a specification.
Katana on the other hand, is fully developed framework made to make a bridge between current ASP.NET frameworks and OWIN specification. At the moment, Katana has successfully adapted the following ASP.NET frameworks to OWIN:
ASP.NET MVC and Web Forms are still running exclusively via System.Web, and in the long run there is a plan to decouple those as well.
On the other hand, IIS is good, resourceful host for web servers. Entire ASP.NET performance issue with using IIS has deep roots in System.Web only. Up until the recent time, when deciding how will you host your web server, you had two options:
So if you wanted a performance, you'd go for self-host option. If you wanted a lot of out-of-the-box features that IIS provides, you'd go for IIS but you'd lose on performance.
Now, there is a 3rd option, a Microsoft library named Helios (current codename) which intends to remove System.Web out of the way, and allow you to use IIS on more "cleaner" way, without any unnecessary libraries or modules. Helios is now in pre-release version, and is waiting for more community feedback in order to make it fully supported Microsoft product.
Systems