The latest major update to Hazel, the file and folder automation tool from Noodlesoft, is here and it's just as invaluable as its predecessor. If you're not familiar with Hazel, it adds abilities similar to email rules and filters — and then some — to the Mac filesystem. On the surface, Hazel 4 looks nearly identical to version 3, but it packs a lot of new power and has some welcome, if hidden, interface enhancements.
A major frustration of Hazel has been figuring out whether you're wielding its immense power properly. There are so many file attributes that can be used as rule criteria, and the number of combinations multiply quickly. Criteria can be combined with Boolean logic (all of these or any of these) and those combinations can be nested; that's just within a rule, and the precedence order of rules matters too!
For a while, Hazel's main window has had a preview mode that shows which rules will apply, but it couldn't be accessed while editing a rule. Now there's in-editor preview, although it's limited to evaluating a single file at a time. No more guess-and-check, accidentally destroying a rule's effectiveness, or having to duplicate a rule to have a "safe" sandbox environment for editing. Hazel rules are set-it-and-forget-it by their nature, and I haven't had any real use cases to create new ones in version 4, but I can tell already how much time rule preview will save.
Another potential time saver in version 4 is rule sync across multiple Macs. Automation is less effective if it needs to be manually set up in every new context. Hazel 4 smartly allows syncing of rules on a per-folder basis. Naturally, if you've got two Macs, they aren't going to have all the same files and folders, but some of the most-frequently automated areas will be on both, such as Downloads, the Desktop, or your Dropbox. This may be more useful for those who have two Macs that both operate in the same context, as I realized that all of my Downloads rules are context-dependent. My home Downloads rules mainly process personal bills, which I never put on my work machine; my work Downloads rules process files that I never access on my home computer.
Even with these enhancements, I feel that setting up rules in Hazel will never be maximally efficient as long as it remains a System Preference Pane. This has long forced the rule editing interface to reside in a sheet and hide subsidiary views in popovers, including impractically small popovers for editing embedded scripts. I long for the day that Hazel becomes its own app, granting access to multiple file preview, rule lists, and rule editing at once — and gaining basic menubar features like proper undo. I've paid my upgrade fee for Hazel 4, and if a standalone app is the future of Hazel 5, I'll be waiting with money in hand.