From the Aldiko Blog (blockquotes omitted):
One question that we often received from you guys is “ Can I separate the books in my library into “read” and “unread”?” The answer is “Yes”. You can actually use Tags or Collections feature in the Aldiko Book Reader app to do so. Below are the instructions:
Go to the list view of your library and then tap on “Tags” or “Collections” (here we use Collections as example).
Tap on the “+” button at the right corner of your device display to add a collection. You will then see a pop-up window, just give the collection a name, e.g. “Read”, and then Select “Ok” to confirm. Follow the same step to create another collection called “Unread”.
Tap on the Expansion icon (the arrow) at the right-hand side of the “Read” collection and then tap on “Add books” to add books that you have already read. Use the same method to add books that you haven’t read to the “Unread” collection.
That’s it! When you want to check out unread books, just go to the “Unread” collection. When you want to check books that you have read, just go to the “Read” collection.
Last but not least, you can follow the above instructions to create “Read” and “Unread” tags as well.
Using Collection and Tag features to separate read and unread books so that you can find your next great read more easily.