Kicking off this week’s must-have apps roundup is an awesome new Twitter client that reminds me of the old (and awesome) Tweetie app — before Twitter bought it and ruined it. It’s accompanied by Camera+, which now supports the iPhone 5’s larger display, and comes to the iPad; an awesome new update to Mixel; and more.

Mixel, a wonderful collage and photo sharing app for iPhone designed by Khoi Vin, has just received what is quite possibly its best update yet. In addition to support for the iPhone 5’s larger display, Mixel boasts a number of new features, the biggest of which is the ability to send real postcards, including your own photo collages, from right within the app.

Mixel is a free digital art and social networking app for iPad. It works beautifully; you and your kids will love it. The only downer is its unfortunate requirement that you link it to Facebook. No Facebook means no Mixel.