App Meteo: Breezy Weather
Breezy Weather is the best meteriology application and is also open source.
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App FTP: FTPClient
A very simple but surprisingly effective program to chat via FTP with servers.
App Mail: Thunderbird
A valid email alternative that excellently replaces all those clients disrespectful of privacy, starting with Gmail, which analyzes and exploits the content of our emails.
Android Repository: F-Droid
F-Droid is a catalog of FOSS (Free and Open Source Software) applications for the Android platform.