I currently use a spreadsheet to keep tabs on my growing collection, and have detailed information on price paid, date of purchase, retail savings, etc.

Ideally I'd like to create a piece of database/cataloging software that has all the features I want, but until I have the time to actually work on it some things I have tried and found pretty good (but not perfect):

http://www.sisimizi.org
Free, open-source, simple, light but highly customizable game collection software

http://www.collectorz.com
Not free, perhaps a bit expensive but lots of bells & whistles, fairly extensive though perhaps slightly less completely customizable

http://www.grouvee.com/
Web-based game collection management. Of the many different web-based offerings out there, I've found this one to have most of the features I'd like and with a decent interface, although not all.

Easy.Get rid of your Steam collection :D

but i havent even played a quarter of the fuckers

Magical Inventory Fairies of course. :P

What I really want is a catalogue app that I can log into whatever digital stores I use and copy my libraries into the catalogue. i haven't found anything to do this yet. But, it must be possible for most sites, yes? Steam's API allows it. GOG's does as well, judging by the wiki library pages. Heck just those two would get me so far toward solving the problem I wouldn't mind doing the rest by hand, especially since so many other sites mostly are places I just bought a Steam key.

I have not looked much for something like it but IsThereAnyDeal deals with my Steam catalogue/wishlist and other people has created scripts to upload my Humble, GOG libraries and other ones. I know some people has recommended other sites...

Haven't played one-tenth of mine. ~.~

I have one word for you...

"spreadsheet"

;-p

Now that you've realized it, next time you go to buy a game on one, check the other to see if you already own it.

Onward from that, it seems like it could be a memory thing? So I would suggest to play some memory-exercise games to get that noggin' joggin'.

Hell. You think double purchases are bad? I've bought second copies of games from the SAME SERVICE because the game looks awesome and I forgot that I have it. INSTALLED currently even... That was embarrassing. Fortunately it was a sale that was too good to pass up.

Between the two platforms I have well over three hundred games. Probably at least two hundred of which are available on both. ^.^ Thats not even taking into account how many games GoG has bundled into single packages.

OP,

I'm all ears for someone that automates the process,,,


As others has suggested a text file or creating a spreadsheet is a way to track your inventory.

The way I do it with each game I purchase since I'm going to have to create a directory for patches, tips, info on the game is I create a directory in which info to that game goes along with:

Screenshots made during the purchase and activation process.
Pdf, and XPS of Receipt for transaction.
Patches
Screenshots found on net for xyx game
Videos found on net that show in game footage as I might buy a game and it be a while till it gets installed.
Info on game, tips

Directory given a name like:
Fallout_3_-_GMG_STEAM_XXXXXXXXXXXXXXXXX

GMG=Place purchased from, EG: GreenManGaming
XXXXXXXXXXXXXXXX= key-activation-confirmation code if no key


*Note for games that have not been purchased, or key has not been used I try to work that into the directory file name.
Additionally for screenshots, the receipts I will edit them with the key code as soon as possible.
EG:
Fallout_3_-_GMG_STEAM_XXXXXXXXXXXXXXXXX_Storepage (showing price)
Fallout_3_-_GMG_STEAM_XXXXXXXXXXXXXXXXX _KEY (Screenshot during prior to activation- with webpage for game pulled up, STEAM being in small mode that shows the "F"s... where Fallout will be once activated.)
Fallout_3_-_GMG_STEAM_XXXXXXXXXXXXXXXXX_ACTIVATED (Ditto, with pop-up showing successful activation, and Client showing game in library.)

Next step is printing a RECEIPT, in PDF, and XPS format for games you manually activate but that feature has been BROKEN since Aug-2014.

http://www.gog.com/forum/general/lets_see_you_can_fiqure_this_out_steam_print_receipt_function_printing_gribbish

Fallout_3_-_GMG_STEAM_XXXXXXXXXXXXXXXXX_RECEIPT


.

Ok, I lied... two words

"spreadsheets and tabs"

Mine has a master list, my games, games gifted, games I will eventually gift, trades, games I have (or will gift my son), and currently, the Secret Santa tab...

I'm usually very religious about transposing every purchase and bundle onto the spreadsheet but not so much lately. I foresee a long weekend of organizing in my near future...

Oh and my game list has title, platform, source and key (I didn't use to keep keys listed but it is super helpful when I go on a total organizing mission...especially since some bundles add Steam keys later on)

I don't look at that the same way. I sometimes intentionaly buy a duplicate if I want a DRM free version. Or sometimes even opposite. *ducks*

What I do mind is having (DRM free) duplicates on GOG and Humble Bundle. That happens occasionaly.