For similar products, you can check the following :
Several years ago (around 2008), we were using Bizflow as our main workflow engine. For some reason, our management decided to make a switch. The alternatives are K2 and Nintex. We ends up using K2 blackpearl, and here are some of the advantages compared to other products :
- Compared to Bizflow, K2 offers better integration with Microsoft products. Two of the killer feature for us are : integrated windows authentication, and integration with Visual Studio.
- K2 doesn't require us to use Sharepoint. AFAIK, Nintex does. And, since we don't use Sharepoint for our BPM apps, Nintex is definitely not the product for us.
PS : I'm not affiliated with K2 or any other product