"Hmm? What's that?" Valve spins around its chair, suddenly noticing the noise. "E3 just happened and we didn't release any trailers for far away, in-development games? Right. Yeah, I guess you're right about that." Valve reaches over and pulls a rusting level by its desk. *k-k-k-thunk* Seventy-five new games have been greenlit, making their way through the community voting process to now have the right to release and sell their games through the service. This batch includes ADOM, Northern Shadow, The Hit, and a ton more obscure games.
These large batches of Steam Greenlight games have become so routine now that it's almost no longer news, but even as the marketplace becomes more crowded, gaining the ability to sell your games to Valve's enormous audience is still a big deal to developers. There are a lot of people who are only willing to buy games that appear on the service, and far more who might not ever even hear of your game if it doesn't show up on the frontpage of the Steam store.
Being greenlit doesn't mean that these games are immediately available to buy, of course. Many are still in-development projects, and securing access now just means the developers can be confident they'll be able to sell their work through Steam when they're ready. It'll be weeks, months or even years before games from this latest batch begin to appear in the store.
You can find the full list of greenlit games attached to the Steam news post, and I recommend you spend some time flipping through. Each one has a linked page with a description, screenshots and most have a trailer, and there's always unheard of gems in the mix.