The following is a list of the cloud services similar to Ubuntu One that work in Ubuntu (Can be installed with a .DEB file) and may provide support for the Unity Systray:
Dropbox
Website - https://www.dropbox.com/
Starting Free Space - 2 GB
Bonus Space - 25 GB to 50 GB when used on an Smartphone
Characteristics - Sync Files/Folders between devices.
Unity SysTray Support- YES
Open Source - NO
InSync
Website - https://www.insynchq.com/
Characteristics - Sync Files/Folders with Google Drive. Extensive Sharing properties. 15 Day Trial.
Unity SysTray Support - YES
Open Source - NO
OwnCloud
Website - http://owncloud.org/
Characteristics - Sync Files/Folders between Devices on your "Own Cloud".
Support - http://owncloud.org/providers/
Unity SysTray Support - YES
Open Source - YES (GitHub)
SpiderOak
Website - https://spideroak.com/
Starting Free Space - 2 GB
Characteristics - Sync Files/Folders between devices. Advanced GUI System & File History
Unity SysTray Support - YES
Open Source - NO
Wuala
Website - http://www.wuala.com/
Starting Free Space - 0 GB Paid Only
Characteristics - Sync Files/Folders. GUI System and an easy way to manage files across devices.
Unity SysTray Support - YES
Open Source - NO
Tonido
Website - http://www.tonido.com/
Starting Free Space - 2 GB
Characteristics - Sync Files/Folders between computers.
Unity SysTray Support - YES
Open Source - NO
TeamDrive
Website - http://www.teamdrive.com/
Starting Free Space - 2 GB
Characteristics - Sync Files/Folders between computers. File Collaboration (Multi User Support)
Bonus Space - Up to 10 GB by inviting others.
Unity SysTray Support - YES
Open Source - NO
SeaFile
Website - http://seafile.com/en/home/
Starting Free Space - 1 GB
Characteristics - Sync Files/Folders between computers.
Unity SysTray Support - YES
Open Source - YES (GitHub)
Syncany
Website - http://www.syncany.org/
Starting Free Space - Depends on which cloud service you use
Characteristics - Sync Files/Folders between computers. Can use Picasa, RackSpace, Amazon, Google, Windows Share and even WebDAV as a repository. Nautilus integration. Advanced GUI. Can integrate with other Cloud Services. Very flexible.
Unity SysTray Support - YES
Open Source - YES (GitHub)
Copy (Barracuda)
Website - https://www.copy.com/home/
Starting Free Space - 15 GB
Characteristics - Up to 5 Devices Synced, 5 GB+ for every invite, Can personalized space provided for a single user. Nautilus integration. Advanced GUI. Can integrate with other Cloud Services. Very flexible. Supports soft symlinks.
Unity SysTray Support - YES
Open Source - NO
Others that may be used (Open Source):
OwnDrive - https://owndrive.com/
- Unified Access to multiple Cloud Services
- 1 GB Free Space
SparkleShare - http://sparkleshare.org/
- Open Source (GitHub)
- Version Control & Privacy
Others that may be used (Closed Source):
Asus Web Storage - https://www.asuswebstorage.com/navigate/
- 5 GB free space
- More free space if you use ASUS Devices
SugarSync - https://www.sugarsync.com/
- 30 Day Trial
- 60 GB Starting Size (Not free)
BitTorrent Sync - http://www.bittorrent.com/sync/downloads
- Offer API to Developers
- Direct Transfer between Devices
BitCasa - https://www.bitcasa.com/
- 5 GB (Upto 20 GB via inviting others) Free Space
- Up to 3 Clients
GoAruna - http://goaruna.com/
- 2 GB Free Space
- Works on many devices
In my case I stick with Dropbox and InSync. Tried SpiderOak and there was a lack of User-Friendliness that I did not use it after a week. InSync is pretty cool (Saves me a lot of time). Lastly Syncany has pretty cool options to connect to other cloud services and even create your own for privacy.