Felltower has had a fair number of cursed items, and a number of items that aren't fully free of downsides.
The cursed items are mostly downside, maybe all downside. Any positive effect is just there to convince you to keep the item or use it long enough to suffer the bad effects.
The semi-cursed items are the ones that are largely upsides, but with a noticeable downside. The major magic weapons of Felltower are like this:
Gram helps you kill dragons, but makes you want to go kill them.
Frenzy is a great axe, but it drives you berserk.
And so on.
Why so many?
Out of Game: Because I like them. I grew up with them in my tabletop games - AD&D - and my computer games - Wizardry, noteably. I feel like they add a nice spice of challenge and concern - magic isn't always just a free benefit. And I was heavily influenced by White Plume Mountain and its trio of weapons with nasty downsides. You want them . . . but they'll change your PC or just change your whole PC's life. Nobody with Blackrazor gets to sleep soundly through the night, trusting and trusted by his or her friends. And I take it as a challenge to make an item so good you'll accept the downsides to get the upsides.
In Game: Because wizards are jerks, and magic is hard to control. The first means they set out to make cursed items out of ill humor, general malice, for vengeance, or for some subterfuge. The second means that even when they don't, sometimes that's what you get.
So in my games, you'll get cursed stuff popping up. Rather frequently.