Forays Into Norrendrin [official site] is a streamlined roguelike dungeon crawler, perfect to fit between the gobbets of work on your desktop, or long dress-up sessions out in the Commonwealth. It's similar to RPS favourite Brogue in that it doesn't use elaborate tilesets to communicate the particular sights, sounds and stenches of its dungeons, relying instead on ASCII figures and lovely snippets of flavour text. It stands out from the pack thanks to heavy use of status effects and exhaustion - it's free.
Development began toward the end of 2011 and the most recent update landed a few days ago. That update added a couple of dungeon types as well as the fantastic flavour text, which sits at the bottom of the screen reminding you that a certain floor smells of mildew, or some other unpleasantness. It's a great touch, managing to provide some character to the randomised spaces as well as embedding them firmly in your memory as you go.
Forays is another example of my favourite recent roguelike variety; dungeon crawlers that relinquish variety and quantity in order to leave the player with a greater sense of control. I used to love games that threw everything at me, including the kitchen sink, but I'm increasingly fond of the more tactical approach to turn-based RPG combat.
That said, there are plenty of creatures in Norrendrin's depths. Many of them require a specific approach if you're to come out of the encounter unscathed. The world is fantastically reactive as well:
"The enemies in Norrendrin are not always the greatest threat to your well-being. Traps can be especially nasty if you're already hurt or fighting some foe, but even a pool of water can be somewhat troublesome if someone uses a freezing attack on you while you're wading. Many types of terrain exist here, and most interact in intuitive ways with existing effects. Because each time you play, the dungeon and its inhabitants are different, you can expect to find many of the interactions through trial and error."
Forays runs on Windows and Linux. It's free.