Subversion is a version control system. Originally designed to be a compelling replacement for CVS in the open source community, it has far exceeded that goal and seen widespread adoption in both open source and corporate environments. The Subversion project produces Subversion's core libraries (written in C), a fully functional command line client (svn), repository administration programs, API bindings for various languages (Perl, Python, Java, Ruby, etc.), and various additional tools and scripts.
CVS is a version control system, which allows you to keep old versions of files (usually source code), keep a log of who, when, and why changes occurred, etc., like RCS or SCCS. Unlike the simpler systems, CVS does not just operate on one file at a time or one directory at a time, but operates on hierarchical collections of directories consisting of version controlled files. CVS helps to manage releases and to control the concurrent editing of source files among multiple authors. CVS allows triggers to enable/log/control various operations and works well over a wide area network.
A tool for editing version-control repository history, reposurgeon enables risky operations that version-control systems don't want to let you do, such as editing past comments and metadata and removing commits. It works with any version control system that can export and import git fast-import streams, including git, hg, bzr, CVS, and RCS. It can also read Subversion dump files directly, and can thus be used to script production of very high-quality conversions from Subversion to any supported DVCS.
OpenGrok is a fast and usable source code search and cross reference engine. It helps you search, cross-reference, and navigate your source tree. It can understand various program file formats and version control histories like Mercurial, Bazaar, Git, ClearCase, Perforce, SCCS, RCS, CVS, or Subversion. In other words, it lets you grok (profoundly understand) the source.
cvsweb is a visual (WWW) interface for exploring a CVS repository. Its enhancements include recognition and display of popular MIME-types, visual, color-coded, side-by-side diffs of changes, and the ability sort the file display and to hide old files from view. cvsweb requires the server to have CVS and a CVS repository worth exploring.
deltasql is a tool to synchronize databases with source code, which helps to keep database evolution under control. While developing mid-sized or big applications, developers make changes to the data model that go along with changes to the source code. From time to time, branches of source code are done to stabilize the code that will go to production. A sort of data model branch is also needed. deltasql provides a simple way to collect all scripts that change the data model and means to handle data model branches. The deltasql server runs on Apache and is backed by MySQL.
ViewVC (formerly known as ViewCVS) is a Python/CGI-based system for viewing and interacting with Subversion and CVS repositories through your Web browser. It can browse directories, view changelogs, generate diffs, view arbitrary revisions, and display annotated ("blame") listings. It has full support for tags and branches, and contains a database-backed query system like Bonsai. It was initially based on the cvsweb work by Henner Zeller, but has been ported to Python and dramatically enhanced.