"Behind the scenes", I approached mcfarhat last week and asked if he would be interested in taking over management of the UI for the block explorer (and later the backend too, once their group has more experience there).

This was because our team has accomplished the main things I wanted to accomplish with the block explorer at this point (fast and lightweight enough for all the API nodes to deploy it, giving us a truly decentralized block explorer). But of course there are many useful features that can be added, and mcfarhat's team was proactively adding some nice features, so his team seemed to be the best one to take on maintenance of this project, allowing me to free up some resources to work on other projects.

The balance and reputation trackers are actually core Hive APIs that the blocktrades team developed. They are designed to be used by all Hive apps (haf block explorer uses both APIs, hivemind uses the reputation API). But again, I think it is good if more teams know how to work on these services, and there is one feature for sure that should be added to balance tracker to serve the needs of both the block explorer and other apps, so this seemed like a good opportunity for another team to contribute to balance tracker. Probably in the future there could be more features as well, it really depends on what needs Hive devs may have.

Regarding Denser, I should clarify that most of the work on Denser will still be done by my team at least in the near term and I am funding it out of my own pocket (well, technically it is Blocktrades the company that is funding it). The actifit team is just getting their feet wet on this project, as we think its good to have multiple teams who are familiar with the code and can contribute to it, and it can give his team some work to do at times when there is no particular feature being added to the block explorer (new feature inspirations often just "happen" unpredictably).

As to Denser's purpose, we are developing it to replace Condenser (the code used for hive.blog and several other sites), using more modern libraries for web design. As you noted, it is open source, so anyone can freely take the code and use it for their own web site, and we are specifically designing to make it easy for people to do this.