Yes, as to local files you can limit access with passwording and with encryption and with (for remote access or LAN access) firewalling or IPTables programming by yourself. Beacuse these abilities are in Linux, though fgotten to differently than via program that does it all(operating system core parts can do this VERY well), they never needed to write a program for that.
I would instead get a copy of the fourth edition of Running Linux-- Publisher is O'Reilly and Associates. Running Linux is a classic, along with the Rute Tutorials (AKA Rute). Worth its weight in gold. Canned apps for this kind oiff thing that you want to do invariably leave holes, knowing how to do this right lets you build very hard to breaks security, and knowing that in fact will make you able to make money doing it for others.
If you want an excellent book on IPTables, one of the devs who helped write the specs for same and built firewalls directly for a living wrote this book:
Title: Linux Firewalls
Author: Robert L. Zeigler
Publisher: New Riders Publishing
more info about this book is at http://www.newriders.com/
If you read this book you will know how to firewall and what firewalls cannot do when done-- keep it as a reference.
Essentially, Linux has trhe trools to do this, but I am not going to rewrite what has been very well written already-- written better than I can now by folsk who know one heck of lot more about this than I. I am only studying to take CISCO certs and then later the LPIC cert series in full. These books (Rute is ALSO a printed book, which helps pay for the free access site bandwidth) are written by people who have already done this, and reviewed by others like them-- the firewalls book was checked for accuracy by a few folks, one of whom WROTE the RHCE tests and was the first RedHat Instructor. they can be used to cross-check what you find on the web-- if they say different, the web site is wrong, PERIOD.
Check out the shorewall, guard dog, and sites for other software under the topic firewall and see how remote access can be limted and access of your users can be limited by IP address, or by DNS caching and only using caching if you really need to limit to just a few sites.
The only good firewall I know for Widnows is Sygate, but Linux has one built-in. Firewalls can control outbound access also, through a box set up as a Linux router which is configured with firewalling. shorewall and guasrd dog are ways to configure IPTables, but you will need to know how to fix also, as guaranteed there will be some learning involved.