I'll post my older idea for implementation for this, but this is still in flux. I'd like to ask you guys how you would like to use such a tool to organize your cards, and what features you'd like from it.
I am currently importing(manually) a decently sized collection. roughly 1500 of these are mine. The other 6000 or so are mine to use, technically on loan indefinitely. The whole purpose for this inventory, for me, is to be able to USE these cards after they are imported, knowing with confidence that, if the actual owner of these cards decides he wants them back, I will have access to a list of 'his' vs. 'mine' and return them. At the same time, the whole point of this loan was that he had all these cards just sitting in a closet and I am an active player. I want to be able to have a physical deck put together with the confidence that I won't have to play "what box does this go into" every time I switch things out. As time goes by, my own collection will be growing because I can't stop buying cards, so the whole process will become more unwieldy over time. This is what I would be using a flag/label system for. As of right now, I am using the mint designation to keep things separate. As I am not a seller or trader at this time, it is working. When I decide it's time to start trading, I have no idea what I'm going to do. So there is my answer for that.
(If anyone has a better solution for my issues here, please let me know. I keep cataloging cards in the hopes that labels or flags are actually on the way, and I know that twisting the mint column is a less than ideal situation. Keeping everything physically separate all the time is simply not a viable option, and I would really like to be able to keep ONE digital inventory instead of two, for geeky reasons)
**Edited to add: I will also have two sons, a son-in-law, and possibly a daughter looking through these things and building temporary decks, as goofy little tournaments have become a thing when the kids come to visit, which adds a whole new layer of "Who does this card belong to" to the whole mess.
On a different topic raised in this thread, I would also like to say that one of the reasons I chose this site to keep my inventory in, is that it is possible to add cards to decks. This way I can log in on my lunch break and brew decks from my phone. That being said, the ability to add a card I only have one physical copy of to several decks is appealing to me, because not all decks I would be putting here will be manual. Some are just in my head.
