This is an interesting, niche utility that, like I2Brain, won't get the attention it deserves.
It's built upon Goldratt's Theory of Constraints and enforces logical (causal - If A THEN B) thinking. It allows for Current Reality Trees, Future Reality Trees and Transition Trees.
Where this is immediately useful is in presentations to Senior Management, who are used to PowerPoints and will be completely blown away by these diagrams.
There are several reference books suggested in the documentation and, while you don't need to read them all, understanding the underlying theory will help you get the most out of this unique tool.
Cross-platform (I only used it on the Mac) with numerous exporting capabilities (to MS Project, for example) I highly recommend it. Some of the functionality must be anticipated (not there yet) such as importing from an xml file generated by MS Project to create a diagram.
Try the evaluation. You'll be hooked.