Cloud was one of the hottest app released for Mac OS X last year. Clever marketing techniques (remember the “every Mac user’s wet dream”?), invite-only beta, a great “Raindrops” plugin system: Cloud app quickly became for many the de-facto standard to share stuff on the web. Whether you want to upload and share links, pics, archives or documents, Cloud is perfect: powered by an elegant web view and beautiful short URL (cl.ly), I’m still using it.

Now you know what’s missing from the Cloud ecosystem: a mobile version. And that’s exactly what Cloud2go is all about: it’s the first unofficial iPhone client for CloudApp.

I was sent a preview build yesterday, but the app is already waiting for Apple’s approval and should be available in the App Store next week. Cloud2go isn’t developed by the Linebreak guys, @phaps is handling it. You can take a look at the app website here.

Cloud2go looks great, and works even better. Uploading files to the internet used to be a hard thing to accomplish on iPhone OS, but thanks to iOS 4 new APIs the developer managed to integrate support for full multitasking with uploads and sync happening in the background. Once you start the app and log in with your cl.ly credentials, you’ll see all your existing uploads organized by file type - the icons depicting them are delicious. Great attention to design.

You can upload files you already have in the Library, or paste directly from your iPhone clipboard. Imagine this combined with Pastebot and you get the idea. Uploads are fast under wifi connection, surprisingly good under 3G thanks to the iPhone 4’s improved upload speeds. You can view any kind of file, including Office and iWork documents, not to mention PDF and videos. The coolest feature, anyway, is the integration with iOS document sharing: say you receive a PDF in Mail.app, tap on it to send it to Cloud2go for direct upload. I haven’t seen this in any other app for iPhone or iPad.

Cloud2go looks promising and, like I said, should be available very soon in the App Store.