The Thecus N5550 has tons of features, and organising these in a logical and accessible manner in the firmware is challenging. Synology and QNAP are a but more adept at this and have a better menu structure. You do pay a lot more for that though.
The standard firmware on the N5550 focuses exclusively on NAS features, and is pretty extensive already. The N5550 supports iSCSI which lets you link a portion of your NAS storage to your computer, which will then function as hard drive instead of network folder. It's also to make ISO files available as shared folders on the network, which means you can use the NAS to burn files onto discs with a connected DVD or Blu-ray burner.
Extras such as download options for newsgroups and Bittorrent support have to be downloaded and installed as modules (separate apps). There are modules for using the NAS as IP camera server, mail server, newsgroup NZB downloader, online photo album and you can also add the Twonky DLNA media server.
More unique modules include McAfee Virus scan and cloud services such as Dropbox and ElephantDrive that you can use as extra back-up. The NAS has a built-in Apache webserver, and you can add the database MySQL as module. The Acronis True Image software bundle is included for making back-ups of your computer(s).