Box.net

It seems, that Nomadesk is no free service
On the following site (1) I can find no information, that nomadesk is free longer than for a 30-day trial period: Nomadesk is the only cloud storage service that includes all of the features below for $15/month for a Team Fileserver and $50/year for a Personal Fileserver. We don't charge per user, nor storage (†). Following the information of (2) you have unlimited backup, but it is not for free.
(1) http://www.nomadesk.com/product/pricing/
(2) http://www.nomadesk.com/product/unlimited-backup/

In regards to"Only with DropBox you can start with 2.25GB free Online storage", Nomadesk offers free online unlimited storage. How is it possible that Nomadesk is able to offer the free unlimited online storage ?

Only with DropBox you can start with 2.25GB free Online storage
With most of the free synchronisation services You have only one or 2GB free Online storage, the same size as with a normal DropBox registration.
But, if you do the DropBox-registration with the following link,
you can start the DropBox Service with 2.25 GB instead of 2.0 GB online storage for free.

https://www.dropbox.com/referrals/NTE0NTExOTI5

This little advantage you cannot get with the free services of SpiderOak, SugarSync, TeamDrive, ZumoDrive or box.net LITE:
SpiderOak: 2GB, SugarSync: 2GB, TeamDrive: 2GB, ZumoDrive: 2GB, box.net LITE: 1GB

Box.net has a definitive targeting of their services to businesses and enterprises - simply reading their description can tell you that much. I don't store much on Box.net simply because I prefer more automated means of file storage and back up. But what I do use Box.net for are the 20 or so different "services" you can attach to your account, many of them are fee based services to the general public but Box.net users can use them for free without having to sign up directly with the service provider when used in conjunction with your Box docs. For instance, eFax is one of the services offered. Faxing something is literally as simple as selecting the document you'd like to fax, choose eFax from a drop menu, and filing in the dialing information. That's it. Their global folders are also cool too, it's like being able to choose your own domain.

See, why SugarSync is different from DropBox, Box.net or MobileMe
https://www.sugarsync.com/sync_comparison.html
SugarSync Desktop application: http://alternativeto.net/desktop/sugarsync/
SugarSync Mobile application: http://alternativeto.net/mobile/sugarsync/