Not marketable on Steam, however games can be packed into a sack of gems (1000 gems) that is marketable on Steam. Also, gems can be crafted into booster packs of trading cards.
Barter.vg tracks your digital game libraries, wishlists and tradables from different stores. You can find users with the games you want and if they've wishlisted your tradable games.
Sign in through Steam to view the users' collections and trades.
⇄ Tradable 155 (9%)
★ Wishlist 67 (4%)
📚 Library 0