* clearing out any items in Downloads > 1week * clearing out any items from my "Temp" folder > 1 day, unless they have an explicit "save" tag ("Temp" is my go-to alternative to the Desktop and is where I stash anything, well, temporary-ish) * automatically moving screenshots into my Temp folder (where they will soon be deleted)
defaults write com.apple.screencapture location /Full/Path/To/Folder2 Time granularity (though you could, I suppose, set up subdirectories in /tmp/ with associated hourly/daily/weekly/monthly cronjobs)
Source code: https://github.com/tdlm/os-x-self-destruct
You can use the OS's standard facilities to do what you want: see `xattr` and `mdfind`.[1] There's also `tag`[2]
1 http://apple.stackexchange.com/questions/93979/are-the-osx-mavericks-tags-visible-from-the-command-line
2 https://github.com/jdberry/tagOn a tangent, that's really what I (and I think most people) want from HSM—not "files canonically being on slow media but being cached on faster media", but rather "files canonically being on small/fast media, and then migrating to slower media when you stop caring about them, as if a garbage-collection pass had occurred, leaving your disk with more space." Basically, HSM should do automatically what people do manually when they e.g. burn files to optical disks to clear up space.
I bet you could set up something similar in it.