TortoiseSVN is an Open Source project developed under the GNU General Public License (GPL). It is free to download and free to use, either personally or commercially, on any number of PCs.

Although most people just download the installer, you also have full read access to the source code of this program. You can browse it on this link https://osdn.net/projects/tortoisesvn/scm/svn/. The current development line is located under /trunk/, and the released versions are located under /tags/.