Engage is similar to Nitro in that it helps you construct Foursquare-like contests and accrue points for particular activities in the sales pipeline.
Engage has a wide variety of activities in its tool chest, including running repeatable challenges and having a dynamic point system that can assess the value of particular sales opportunities. You also can have multiple games going on at the same time within a single enterprise, say if you want to have different challenges being run for different workgroups or branch offices. You can see an example of their full user profile with a sidebar with daily/weekly goals and challenges is present on every page. (click to enlarge)
Games can be a way to distill a series of performance metrics down to a single numerical scale. They also can clarify how a sales team should be motivated when they are being compensated with complex commission formulas or have multiple opportunities to close customers and have to prioritize their time. One of their clients stated, "social conversation between reps changed from Fantasy Football to sales metrics in the first week we were using Engage." That is serious business, to be sure.
Engage has been in beta for several months, and their largest client has 400 Salesforce licenses. Some larger installations will be announced next week at the Dreamforce show. Pricing will be $25 per user per month.