To quote the DarwinPorts [http://www.opendarwin.org/projects/darwinports/] FAQ:

DarwinPorts is probably best described by comparison:  It's sort of like the [FreeBSD] ports collection or [fink] in that it automates the process of building 3rd party software for [Mac OS X].  It also tracks all dependency information for a given piece of software and knows how to make it build under Mac OS X and install it to a common location, meaning that software installed via DarwinPorts doesn't simply scatter itself all over the system or require user knowledge of what to install in what order. 
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DarwinPorts is written in [Tcl]!
DarwinPorts also builds and (mostly) works under FreeBSD, [OpenBSD], [NetBSD], [Solaris], and [IRIX].
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New Tcl-based GUI to manage DarwinPorts packages: [PortAuthority]