They seem like all mathematical algorithms for root finding, integration, etc. Very interesting though. Do the zip files contain more information about each algorithm, or are they just code. It would be amazing to have a wiki that had each algorithm and alternatives listed.
Yup, they're all numerical algorithms (er, at least almost all; I haven't checked anything like every single one). They started out in the ACM Transactions on Mathematical Software. The amount of information you get along with the code is variable, but often small. The code is all too frequently in FORTRAN, too, especially (of course) in the older algorithms. But there's some very good stuff in there.
If you keep scrolling there are some more non-pure-math algorithms. Including: pathfinding, heaps, and some threading stuff.
I like the reverse chronological order... It's like being transported back in time, and watching the history of CS fly by in fast-forward.