Recently launched, minimalistic, and highly focused:

BrainStorm [brainstorm.naviance.com] is an interesting tool written in Rails for web based collaboration. You can create Conversations and invite others to participate. It’s still a little bit buggy but quite interesting, since you can add a variety of content fragments – appointments, checklists, ideas, quotes, reminders, tasks, and so on:

Pixoh [pixoh.com] is an online photo editor. Currently it lets you resize, crop and rotate photos, but more features are on the roll.

ShortText [shorttext.com] lets you publish microchunks of text on the web. Each fragment gets its own (short) URL. Nice.

Last not least FeedSifter [feedsifter.com] lets you create filtered feeds which only let pass items containing specified keywords. This is handy if you want to scan many feeds for specific topics only.