TortoiseSVN is free. You don't have to pay to use it, and you can use it any way you want. It is developed under the GNU General Public License (GPL).

TortoiseSVN is an Open Source project. That means you have full access to the source code of this program. You can browse it on this link http://tortoisesvn.tigris.org/svn/tortoisesvn/ . (Username:guest, for password hit enter) The most recent version (where we're currently working) is located under /trunk/ the released versions are located under /tags/.