TrueNAS (formerly FreeNAS but got a rebrand). Built around ZFS and FreeBSD, it's a really solid and more focused NAS product. DSM has more general features like

TrueNAS (formerly FreeNAS but got a rebrand). Built around ZFS and FreeBSD, it's a really solid and more focused NAS product. DSM has more general features like their whole surveillance software and such, but with a touch of irony NAS for important data is the main thing I didn't ever trust Synology for given the lack of ZFS. TrueNAS can do some other stuff but primarily it's about doing NAS right and fast, and if you want something dedicated to that role and more turnkey (obviously you could just set up any system with Linux and ZoL or FreeBSD naked and NFS yourself) it's well worth a look. It's BSD license, and iXsystems is the primary developer behind it. They do offer some of their own hardware, so you can get a similar "commercially supported buy and turn on" experience to Synology if you'd like, though I don't think the value proposition from them right now is the best for home users or certain SMB. But it's there. And unlike DSM there's no workarounds needed to run it wherever which is another huge tick in its favor IMO. With something as critical as a NAS I don't mind paying a company for support or hardware, but lack of official easy exit options makes me nervous. For reasons like, well, this?