It seems that Google Groups does not accept my post for some reason, so here are some additional details on this project.

I plan this to be a PDF reading and annotation tool, which will sync with the Zotero server. All libraries will be read only (no adding or editing of items, collections, etc) except for modifying already existing PDFs. I do not plan to support tags at all and saved searches are not planned for the 1.0 version. The source code is available under an open source license and I plan to release this as a free app in the App Store when it is ready. However, if someone who joins the project would prefer it to be a paid app, that would be ok for me as well. 

The following features have been implemented:
-The App comes with a very small built-in demo database. This can be replaced with a real Zotero database using iTunes file transfer.
-Browsing library and collections tree (shown on the left in the image)
-Showing items and thumbnails of PDFs for the selected collection

What has not been implemented:
-Sync with Zotero server
-Search and Sort
-Clicking an item to view the PDF 
-Better formatting of items in the list (a CSL parser for Objective C would be great)

Also the code needs to be optimized a lot further than what is currently is.

Great job! I'm glad to see this happening, and I'd love to help out in any way I can, short of actually developing, since I don't have a Mac or iOS device to work on. And when I buy my next Mac, I'll start coding for this too.

Hopefully some others can help out in the meantime, and good luck bringing out the first release. You may also want to keep an iPhone interface on the roadmap, since this would be quite useful for the many iPhone users as well.

Judging from the responses I've seen to Zandy, I'm pretty sure there are people who find it pretty useful, especially for smaller what-was-that-paper? moments. Less so for reading PDFs, obviously, but just having the references is something like Qnotero for your pocket.

Very exciting. I do hope ZotPad will support offline work too. One of the prime use cases I imagine will be putting papers in a collection and reading and annotating stuff from that collection on long travels or other offline moments. The expectation would then be that the annotated PDFs could be synced back to the Zotero server.

The current development version supports offline use for reading. There is still a couple of days worth of work left, but it is possible that we can submit ZotPad to app store before the end of the year.

The first release will not support annotating because Zotero does not yet support uploading files from third-party applications. The features are roughly the same as in Zandy.

The long term plan is to allow two different workflows for annotating
1) "Send" documents from ZotPad to iAnnotate or any other software that is capable of receiving PDF files and then "sending" these back to ZotPad
2) Annotating directly within ZotPad

If ZotPad is in offline mode, the annotations will be stored and synced to the server the next time network connection is available. But all this depends on Zotero implementing file uploads from third party apps.

Just a short update. I will work on this some between christmas and new year, and hope to submit the app for review once Apple app store staff come back from their christmas break.

The app now has most of the "difficult" parts implemented now, but needs a few optimizations here and there. What needs to be implemented still is downloading attachments files from the server, but this is straightforward.

I have now another developer, who has joined (or at least planning to join) the project. He is one of my coworkers at Aalto University. We plan to release this as a paid app that is priced at the same leve as Zandy for Android, which is 3€/4$

In the future we might release a premium version with built-in annotation capabilities using the commercial iAnnotate library (http://www.ajidev.com/iannotate/developers.html) Since we need to pay a license fee, what ever cost that will incur for us will be added to the price of the app for the premium version.

If someone is interested in working with us, we are happy to share what ever revenue this might generate. Also, if you have an apple developer license, you can check out the code at any time at github and install it on your iPad.

The first version most likely will not support iPhone so that we can get it out as soon as we are satisfied how it works on the iPad and can concentrate on the iPhone version after that.

How iOS works is that Applications can register as being able to receive documents of certain type sent from other applications.

ZotPad will send PDF documents to any application that can receive PDF files. (It would be more difficult to try to restrict this to a particular application than include all.) So GoodReader will be supported.

The iAnnotate library is a future idea, which I think that some users find useful because it reduces the number of steps needed when doing annotations.

The first version will be a one-way street because Zotero does not support file uploads from third party clients. Once this is added, I it will be a two-way system.

How this will work is that ZotPad will register itself as a receiver for PDF files (and later maybe other files) and you can send files from GoodReader to ZotPad the same way that you send them from ZotPad to GoodReader. Then ZotPad will use the filename to detect which item the file belongs to, and will replace the existing file in cache and upload the new version to Zotero server.

But this depends on when Zotero implements third party uploads, which should be soon. Also there are some plans to make ZotPad and Zandy to sync with Zotero on a local computer without using Zotero servers.

Just read the Zotero dev discussion and the ZotPad description. Exciting.

In the dev thread it is pointed out that downloading the whole library or downloading on demand are not the only options. But no good example is given of a possible middle ground solution. Here is one. Call it the podcast model.

Allow the user to designate one or more collections (possibly with subcollections) as the "ZotPad Reading" collection. Call this subscribing to collections. Automatically download everything contained in the subscriptions to the device. Don't have me download the whole library to my device if I don't need to.

This would fit the use case of (offline) travelling very well. Items to read would be like podcasts to listen, auto-updating based on collection subscriptions. Indeed, taking the podcast metaphor further, it would be great if ZotPad would remember (1) my position in a file and (2) my reading history.

In the dev thread Dan worries about the amount of API calls needed to replicate a whole library offline. But from the perspective of the user, too, there are good reasons to allow users to download only a selection. My library is over 20Gb and I think many libraries may be like that. I don't need to have all my 6000+ items on my iPad. If I travel for a few days I know roughly what I want to read. The podcast model (readcast? zotcast?) allows me to download selected collections to my device — ten to a couple hundred items maybe — and helps me to get my reading done. Users would love it.

I am excited about ZotPad, and can't wait to hear updates. In the meantime, I am trying out the solutions described so far in this thread...

Just a quick update: Changing the software to use the new API functionality was a bit more work than I thought, but it is now done. I will have time to look at the code next time toward the end of the week and hopefully submit it to app store review as well.

I am not going to implement any other cache preferences at this point because the software is close to release, and this would cause a delay. There will be more detailed cache options in later releases based on user feedback. Something that you suggest will most likely be implemented at some point.

Whow great job mronkko! If I may chip in my two cents here, I'm afraid my own needs are a bit more modest. I primarily use Zotero to keep my bibliography, and not for cataloging pdfs, and it would be great to be able to see my bibliography, edit entries and add new entries on my iPad. For instance, I include notes on the entries in the summary and it would be useful to access those notes wherever I am. As I understand the description of your app, this will not at all be possible right? I would only be able to see my library, not edit nor add, correct? Is this because it will be difficult to implement this technically, or is this just because you had a different focus with this app (and maybe we can expect it to come in the next app-update)?

Anyway, again, great job, it looks delicious and I am sure many people will want to use this. Would love to hear your comments on my questions.

What are the plans for webdav support for the attachments in ZotPad? I managed to compile and install the current version of the source code and when I got no pdfs displayed I realized it's probably because all my attachments are stored on webdav. :)

I searched the code and noticed a TODO relating to webdav. What's the plan? I might be interested in helping out but I am new to objective c and ios development so it might be slow work. :)

I appreciate you working on this, I'm currently a MA student and am really glad to know someone is working on this as it will be very useful and helpful... thanks for all your work