x42 Protocol is not as old as you mentioned, but they have maintained and updated the coin for two and half years, probably the most active github I've ever seen. Worth a look.
Yes, if we look at maintenance for two and a half years is not such a long term, but the important thing is at least they are still working on it, and for the issue of feasibility to look at at this point is the Bitcoin bullrun going on, because it is much more profitable.