Since Airmash was released on HN, this is as good as any place to put out a message for the original developer -- we love your work! Is there any chance we could continue it more officially in your stead?
The biggest issue is that no free frontend exists, and even if it did, some aspects of reimplementing both backend and frontend have interesting problems, such as in the functions to calculate trajectories and the data they use. There is no way to replicate the original Airmash without preserving almost exactly this code. It would be amazing to receive your blessing at least to borrow these aspects.
-- (every Airmash addict ever, especially those racking up hours almost every day even after the official server died)
There are currently 2 replacement server implementations, the first was done in Rust ( https://github.com/steamroller-airmash/airmash-server ) powers (I think) all the US servers. It is missing some features like upgrades.
For that reason most of the 'life' is on EU servers, despite the increased latency for US players, which are using a newer and slightly more complete Node.js implementation ( https://github.com/wight-airmash/ab-server ). If you're trying it out, be sure to check out EU.