Re: Studio inventory app?
As Carol stated, spreadsheets.
I recommend Apple Numbers or Google Docs' Spreadsheet. Google works on every type of computer or tablet. The reason being is that while DataViz Documents to Go is a lovely thought, you have to pay to play, and it can get expensive when you need the add-ons. This is also true for Microsoft with their current monthly fees.
I like Numbers because you can add photos to the spreadsheet itself, so when you are doing painting and drawing inventory, you can have a reference photo.