You can filter your games by unused keys and by platforms. To use the unused key filter, go to the "Games" tab on your purchases page and select one or more of the options under the "Key filter" group. This will limit the results to products that include all the platforms you selected, and contains unused keys. If you want to filter for games that contain DRM-free downloads, select the operating systems you want to filter by under the "OS filter" group. The games with all the OS's you selected will be displayed. You can also combine both filters, resulting in games with all unused keys for platforms you've selected and have DRM-free downloads with the OS's you've selected. Use the search box to further narrow down you results.
An unused key is defined as a key that have not been revealed, have not been marked as used, and products that have not been revealed and contains keys.