Synology has dozens of packages, these are the once to install and look at first
Synology has a massive amount of great packages all held within the package center, to the point where it can be overwhelming. This is not an exhaustive list of all of their packages, but rather the packages that most people will get some use out of.
Synology Snapshot replication is quite honestly the very first app that you need to install. Snapshots are a feature that are only available on BTRFS file systems. Most Synology's now have BTRFS, but if you have an EXT4 volume, this will not work.
Snapshots are a feature of the BTRFS file system that allow you to include versioning within your file system. This allows you to easily see old versions of files and even restore them. This can protect you from ransomware or even just an accidental deletion. For example if an employee saves over a critical file, using snapshots makes it really to restore.
Hyperbackup is Synology's primary backup application. It allows you to back your NAS up to multiple different sources, including:
as well as just about anything else you can think of
This is something that a lot of users will often overlook, as they thing RAID is a backup, but RAID is NOT a backup, as all of your files are deleted at the same time off of all of the drives. I recommend the very first purchase most NAS users buy is an external hard drive like this (affiliate) and then set it up as a hyperbackup task as covered in this video.
Synology Photos is an application that can replace google photos or iCloud. It can backup your photos directly from your phone with their mobile app. It includes local facial recognition. It has the ability to have multiple users to each have their own "personal space" then also having something called the "shared space" which you can use as a group family photo album.