Hero is one, it appreciates 5% per year pegged to the USD. Arguably altcap.xdr which is a basket currency could be considered an algorithm based asset since it has a formula behind it, though AFAIK the calculation is done on the IMF's side.

There has been talk of the opposite to hero, an asset which depreciates x% per year which would actually be quite simple to implement as an ABA.

Do you have any ideas for an ABA?