i wan to use owncloud with "small workgroups or departments". I want to kown how many users can access owncloud concurrently?
my server with 12 CPU cores,32GBRAM,using CentOS6.5,and my database is MySQL 5.5.51.
there are no restrictions / limitations of concurrency in ownCloud. Everything is limited by the hardware specifications and operating system and database optimization.
As you might note its not really possible to give numbers so you need to do a test setup and do some research on your own.