It can be anything from a webserver serving the admin web dashboard or a more traditional desktop GUI.
In terms of features I would expect being able to:
- manage systemd services
- manage mounted disks
- managing the filesystem(and all the users/permissions/groups concerns), especially with ACL in mind
- update/upgrade/package-management(install/remove)
- SSH console in case it's not running on the server locally
- (optional) handling encrypted partitions(boot/root/external)
I'm even willing to pay for it, given a price for a solo SysAdmin and it's middle/low tier servers.
ps: I know that many would suggest to learn the terminal way and be content with it and I already do like this so far, but I just want to ease my life from this point of view.