The current version is 20050331.
Releases are available as a source archive and precompiled binaries for several common platforms from the GPC web site, http://www.gnu-pascal.de.
For details about new features, see the section News on the web site. On bugs fixed recently, see the Done section of the To-Do list (on the same web site).
GPC uses GCC as a back-end. It supports GCC version 2.8.1, 2.95.x, 3.2.x, 3.3.x or 3.4.x. (The newest supported GCC version is usually preferable, unless it contains serious bugs in itself.)
There are no fixed time frames for new releases. Releases are made when enough interesting changes have been made and the compiler is somewhat stable.