What is Aldiko?
As the excerpt already states, Aldiko is a famous ebook reading app. It often comes pre-installed with devices, especially if the device is a tablet. Differences between the Aldiko Book Reader Premium and the Aldiko Book Reader Free are: the Aldiko Book Reader Premium has highlights, notes and home widget features, gets faster update and does not contain advertisements. Both support the formats epub and pdf, and can handle drm protected/crippled books.
Similar to moon-reader, Aldiko can access online book shelves. It does this directly via their websites (not using the OPDS standard), and even permits to shop/buy books from within the app.
Where should I use this tag?
Only if your question is about this specific app. If it's for another app, or about ebooks or readers in general, please check with the ebook-reader tag and the "related tags" section in its tag wiki.