There are several major sources of Open Source (ish, we won't worry about strict definitions here) applications. Some are:
fink is a bit better established, and uses a Debian-like mechanism: "fink selfupdate", "fink update-all", etc.
MacPorts is more like FreeBSD; in fact, the founder came from FreeBSD.
The NetBSD package system is multi-platform.
MikePatterson is currently examining possible ways to integrate this with xhier. See
MacPackageViews.
There are currently no local repositories for either packaging system, although I've started looking at keeping locally-built copies of unstable fink packages (for no better reason than it came first and it's what I use on my Powerbook).
Intel
MacPorts fully supports Intel Macs and Leopard out of the box. fink supports Intels, but installation for Leopard still requires bootstrapping it from source.
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MikePatterson - 10 Apr 2006, updated 20 March 2008