Overall this looks like a very strong release, especially with some of the core engine enhancements around temporal reasoning, support for XSDs and delarative type modeling. If the commercial vendors did not think they had a real competition on their hands, Mark and his team will prove them wrong with 5.0. Drools 5.0 is not yet ready for release (they are hoping for a November release) but those of you who like playing with, and contributing to, code that is nearly ready can get it from the downloads page (scroll down). Michael Neale posted Drools 5.0 M2 New and Noteworthy Summary recently and Drools 5.0 M1 - New and Noteworthy before that. You can get periodic updates on the world of Drools from Mark and Michael on their blog.
RuleXpress is a repository-based tool that can be used offline or in a multi-user environment. Models are stored in a central repository and can be checked out to a local copy and then merged back. Within the tool the key organizing principle is that of a community - a group of people who share the same understanding about their vocabulary and rules. Within this you can have projects but the focus of the tool is on the activity of vocabulary/rule management as an ongoing task. The key activities are to manage vocabulary and rules or, more specifically terms, fact model, rules, decision tables and rule groups.