For developers, it could be a good source of extra income. That said, some developers have reported huge download numbers off the back of the free app of the day promotion, but no resulting increase in sales once the promotion is over. You are also likely to do better with tablet optimized apps than smartphone apps in general, as Kindle users are the primary customers. Droid App
File browsing is something everyone inevitably has (or wants) to do, so you might as well do it with a capable, fantastic file browser. Solid Explorer is pretty much as good as it gets in the file explorer apps realm. It features Material Design, archiving support, support for the most popular cloud services, and even some more power user stuff like FTP, SFPT, WebDav, and SMB/CIFS support. It looks great, it’s incredibly stable, and it just works well. There is a 14-day free trial with a $2.99 price tag at the end of it. This is, by far, the best file manager on Android for most people. Droid App
Network Analyzer makes it easy to view information about all of the Wi-Fi networks nearby. With a few taps, you can see the strength of networks in the area on a dynamic graph and view detailed information about your connection, such as your IPv4 Address, MAC Address, and Default Gateway IP. You can even run a network query from within the app; it lets you Ping an IP/Domain Name or even check the DNS Server settings. It's the perfect companion to our article on how to find your IP address.
Airbnb should be your go-to app for finding rooms, apartments, homes, and other unique accommodations when traveling, if you don't want to go with a traditional hotel. The length of your stay need not be short-term either; some locations let you book a stay for several months, which may appeal to people working temporary jobs in new places. This travel app also highlights other experiences and restaurants, so you can find out about everything a locale offers. Droid App
Weather Underground combines a slick design with a focus on really useful weather information. We particularly like the ability to report weather conditions in your area and the extremely useful comparative forecasts that deftly show how conditions have changed since yesterday. With an accompanying set of useful widgets, it's the best weather app on Android. Droid App