FWIW - I (also) use Excel on my MAC, partly because I already have Excel and know my way around using it (so no learning curve) and partly because I didn't turn up anything that seemed to be much better in my, albeit not very extensive, search. I did consider trying Bento, which was Apple's 'version' of Filemaker, but just about the time I was going to try it out, Apple had bailed out on offering it/supporting it. The learning curve for Filemaker seems pretty daunting - especially considering my relatively simple needs.
One advantage of Excel is that its fairly easy to manipulate (e.g., sort) and expand as needed. My spreadsheet has several tabs - the master list and then several worksheets (tabs) with different sorts on that master list - e.g., car type, road name, repairs needed, etc. Of course, this means having to recreate the sorted lists every time the master list is added to or changed. In my case, I have a yellow-highlighted box at the top of each worksheet that has the date that particular worksheet was updated - so the master list may get updated all the time and the sorted lists lag that. As I suspect most of you know, one can do a sort on multiple columns. As you will see below, most of the entries in the different columns are text (for which Excel does an adequate sort), so one has to be consistent in the various names and descriptors if you want them to show up in the same place in the sorted list - for example, CB&Q vs Burlington vs BN vs BNSF
Here are my column headers in the lists:
Number (this is usually the manufacturer's catalog number)
Category - locomotive; freight; passenger; Maint. of Way
Type - diesel, steam, box, flat, cattle, baggage, crane, etc.
Description - Atlantic, FEF, PA, depressed center, heavyweight, etc.
Smoke/choo-choo - denoted with an x (not all my Flyer inventory has these)
Action? - denoted with an x (e.g. a box car that tosses out boxes)
Road Name
Condition - something like what TCA uses (probably not well calibrated to TCA..)
Manufacturer - Gilbert, Flyonel, SHS, Am Models, etc.
Manufacture date (est)
Acquisition date (est)
Cost - most of this is based on what I paid on eBay or at a meet
Notes/comments
Picture - denoted by X (I guess there is some way to make a live link...)
Repairs done
Repairs needed