Not sure if Synology (Xpenology) NAS supports OwnCloud but I use that as a repository for all my photos etc. On each client (Laptop, phone etc) you install an OwnCloud client which keeps all you devices in sync. If you don’t want to use the client app you can still access your media via a Web page. Best of all its opensource! If your cleints need to connect from outside you home network you may need to setup port forwarding on your router. If you do need external access make sure you setup HTTPS on your OwnCloud web services, it defaults to using http (data is passed unencrypted i.e. passwords).
See
https://owncloud.org/ and
http://forum.synology.com/enu/viewtopic.php?f=190&t=90744
Theres even an app in the iphone store.
One note of warning!!!! If you delete anything off one client it deletes off all the others, including your NAS. You may want to restrict some users to Read only access?