I used BeOS as my main driver for about a year and a half, back in the day.
One thing that we take for granted now was it supported low-latency concurrency, so its user interface felt really, REALLY snappy. You could launch 4-5 different videos, in different windows all playing at once, and there was absolutely no jitter and lag. Unless you grew up with the user interfaces of the mid-90's (Windows 3.1/95, MacOS 7.6), you won't appreciate just how mind-boggling this was.
The other big feature that unfortunately hasn't been broadly adopted by other operating systems was the file system. I know this one pretty well because I actually wrote my own driver for it (as a high school's hobby project mind you, so probably extremely cringe if I saw the source code again). BeOS didn't have a hierarchical file system so much as a relational database with built-in support for showing nested relationships as folders, and support for multi-megabyte blob types for the actual file data. Emails, for example, were stored with each header value as a separate column in the email table. If you opened your folder of emails, you could sort by sender, time received, subject, etc. just from the finder window. Within the BeOS API, you could write complex joins on the filesystem, e.g. between your emails and your contact list (which was also stored as metadata IIRC).
One thing that we take for granted now was it supported low-latency concurrency, so its user interface felt really, REALLY snappy. You could launch 4-5 different videos, in different windows all playing at once, and there was absolutely no jitter and lag. Unless you grew up with the user interfaces of the mid-90's (Windows 3.1/95, MacOS 7.6), you won't appreciate just how mind-boggling this was.
The other big feature that unfortunately hasn't been broadly adopted by other operating systems was the file system. I know this one pretty well because I actually wrote my own driver for it (as a high school's hobby project mind you, so probably extremely cringe if I saw the source code again). BeOS didn't have a hierarchical file system so much as a relational database with built-in support for showing nested relationships as folders, and support for multi-megabyte blob types for the actual file data. Emails, for example, were stored with each header value as a separate column in the email table. If you opened your folder of emails, you could sort by sender, time received, subject, etc. just from the finder window. Within the BeOS API, you could write complex joins on the filesystem, e.g. between your emails and your contact list (which was also stored as metadata IIRC).