BitcoinJ: Very old client from back in the day
Still has a team maintaining & updating it (driven by Andreas Schildbach's work on Bitcoin Wallet on the Android Operating system), but it shouldn't be on this list, because:
- Cannot be used for a full validating node (validates block headers only, then resolves transaction validity using BIP37 bloom filters)
- Is only a library; does not function as a standalone, executable Bitcoin client
Indeed, I thought it was abandoned.. and well it's just an SPV client, so I guess I will edit the list.
https://coin.dance/nodes already provide all Bitcoin clients with each client info, total nodes and it's history and feature the clients have. I'm not sure how accurate this website though.
The only active client's developments beside Bitcoin Core only BitCore and bcoin which usually only useful for developer.
That website is pretty inaccurate. For instance, the TRB client, is listed as supporting "Emergent Consensus". As far as I remember, EC was some sort of Bitcoin Unlimited-Gavin trickery.
I forgot to add this one in the list.
But in any case, im sure there are other ones not listed there, maybe some obscure dev teams doing something under the radar, that is what I find most interesting.