So I found an interesting way to sort items via turtle a while back, and only now got around to posting it.

Now there are already a number of ways to sort items. For example, a chain of turtles who each does a quick compare, and, failing that, passes the item on to the next in line. While this is probably the fastest way possible to sort items, it's also fairly expensive, hard to relocate, and sometimes quite laggy.
Another way is to have a single turtle going down a line of chests, pulling out a single item to compare, puts it back, and moves on to the next. While really cheap, this is probably the slowest way of sorting, and you can't put the chests next to each other.

My method ( discovered back before printers were a thing) is much like the chest method, but instead uses furnaces.
Yeah, that's right, furnaces.

Basically my method exploits that furnaces are effectively 3 1-slot inventories. If an item can't be dropped in that single slot, it obviously doesn't match the item in there, so we save time with inventory transactions.
You can just run a long line of furnaces to sort with… And one 2 blocks above that. This can be even more dense than an iron chest setup because you can easily use both the top and bottom inventories of each furnace.

Of course a major drawback is that you'll have to keep your storage elsewhere. :P/>
And you have to constantly switch slots to sort more than one item type at a time, although this can be avoided by simply sorting a large amount of one item type.
EDIT: it can't sort unstackable items either. (Not sure if compareTo works with tool damage…)
EDIT2: yeah and obviously be careful where you put fuel.

Hope this was useful to somebody :)/>