there are two category of full nodes in my opinion.
- bitcoin core and the alternatives that are built on top of it and have additional options.
so this category will contain bitcoin core itself, Armory, bitcoin knots, ...
- the standalone full node implementations that do not depend on bitcoin core.
there are a couple of them. like
gocoin, and i believe
StratisBitcoinFullNode is that way too. there are some others that i am not familiar with either.
the problem is that the first group are popular hence it is the safest option because popularity also means more reviewed and bugs are found. but the second group is less popular and have a high possibility of having bugs.
as for others that may look like bitcoin nodes (like unlimited), since they are designed to enforce different consensus rules you can not categorize them as bitcoin nodes.