A standalone tool for updating applications in the field.
This was a crucial piece of infrastructure to me, back when people would install a video game off a disc, and then later manually download patches for that game.
This was used for several Mac OS X titles I worked on. This code would likely need some updates for modern systems (it used the Carbon API, which is a giant no-no in these later years, for example), and with some small effort could likely target Windows and Linux as well.
But in an age of broadband, package managers and app stores, it's not clear to me any maintenance on this package is worthwhile now.
If you need it, though, feel free to steal what's useful. And I will always accept good patches.