Sun Microsystems developed several enhancements to Solaris:
In the early days (where it was named SunOS): NFS, NIS, automounter.
These were licenced by other Unix vendors. And so became de-facto standards.
Linux re-engineered them.
Later enhancements were
/proc and ptools (pgrep, pkill, ...),
RBAC (roll based access control, could replace the static UID 0 superuser model),
doors (a simple IPC mechanism that Solaris used because its socket implementation was slow),
SMF (service management facility, replaced the SysV init files),
configuration registry (a DB replaced /etc files),
ZFS (replaced the UFS-based file system and volume manager),
live upgrade (patches on a new file system root).
Despite the changes Solaris always sticked to the
Unix principle: do one thing and do it well. For example the SMF cares about services: startup, shutdown, supervision. Its development is complete, it does not evolve /creep into other parts of the OS.
In Linux there is another philosophy: a piece of software is never complete. If development stops then, even if it works well, it must be timely replaced; often a security risk is anticipated.