This week we’ll search for photos of hotdogs with Retrobatch, hike the Appalachian Trail with Gaia GPS, and learn foreign with the new Duolingo.

Retrobatch

Retrobatch, from the developer of Acorn, is a batch-processor for images, letting you build simple or fancy workflows that can do pretty much anything to your images, automatically. If you regularly resize photos, remove location data, add watermarks, or anything else, this is for you. It can even look a the images and see what’s in them, letting you only process images with hot dogs in them, for example.

Right now, Retrobatch is free during its beta period, and can also be purchased for $30.

Duolingo

Duolingo turns language learning into game, with goals, streak, and rewards. You can, for instance, use your earned Lingots to buy a gold tracksuit for your avatar, a green owl-like creature.

In this new update, the app doubles the amount of “learning content, and also adds a new kind of deep-dive feature, that lets you focus on particular subject areas, like food or travel, or grammatical subjects, like irregular verbs. Choose from any of 27 languages, including English.

Price: Free with in-app purchases

Download: Duolingo from the App Store (iOS)

Icro

Icro may do for Micro.blog what Twitterific did for Twitter, taking it into the mainstream. It’s a universal iOS app for the Micro.blog social network, and it will look instantly familiar to anyone who uses Twitter. That’s not to say it’s derivative. Just that it brings your timeline, you favorites, and so on, into a familiar interface that’s easy to browse, and great to look at.

It’s also free, which means you should check it out immediately.

Price: Free

Download: Icro from the App Store (iOS)

Gaia GPS adds NatGeo Maps

If you do any outdoors activity more strenuous than tending the backyard grill, or schlepping all the way out to the car, you’ll probably know Gaia GPS, easily the best map app for iOS (and the web). This week, Gaia has released an update, not to the app itself, but to the maps available in-app. Now, if you are a premium subscriber, you can access the National Geographic John Muir Trail maps, and the NatGeo Appalachian Trail maps. The maps themselves look gorgeous, bit more importantly they include “detailed topographic information, clearly marked trails, recreational points of interest, and navigational aids.”

Price: Free with in-app purchases

Download: Gaia GPS from the App Store (iOS)