Open Source Software for Android
K-9 Mail
K-9 Mail is an open source email client focused on making it easy to chew through large volumes of email. K-9 Mail is designed for both novice and power users and offers lots of features for everyone. It provides features like Push IMAP Support, GPG & PGP/MIME support, Per Account Notifications, Unified Inbox, White and Dark Theme, and Signatures.
Zulip
Zulip is an open-source real-time chat with an email threading model. With Zulip, you can catch up on important conversations while ignoring irrelevant ones. Zulip provides modern apps for every major platform, powered by Electron and React Native. The software is 100% open source software, built by a vibrant community of hundreds of developers from all around the world.
Master Password
Master Password is password manager based on an ingenious password generation algorithm that guarantees your passwords can never be lost. While most password managers store your passwords on a server or your local device, Master Password generates unique passwords on the fly, based on your username, the site or application and time. This approach makes Master Password safer from loss, theft, problems with backups, sync, confiscation, snooping, and more.
LessPass
With LessPass you can manage your registrations, login and passwords with is. LessPass is a password manager that computes a unique password using a site, login, and a master password for you mobile Android or iOS device or as a browser extension for Google Chrome and Firefox. Since a password manager, or any software for that matter is as secure as it is transparent, the LessPass source code is available on Github and can be inspected and perfected by anyone in the community.
Keepass2Android
Keepass2Android is a password manager application specifically design for your mobile Android device. It allows to store and retrieve passwords and other sensitive information in a file called "database". This database is secured with a so-called master password. The master password typically is a strong password and can be complemented with a second factor for additional security. The password database file can be synchronized across different devices. This works best using one of the built-in cloud storage options, but can also be performed with third-party apps. Keepass2Android is compatible with Keepass 1 and Keepass 2 on Windows and KeepassX on Linux.
Internxt Drive
Internxt Drive is a secure file storage solution with a focus on user-friendliness and security. Internxt Drive allows you to store files, photos, videos in the cloud and sync or backup local files and make them available for sharing online. With Internxt Drive military-grade encryption you can rest assured that your files are in safe and only accessible by you.
Wallabag
With Wallabag you can save web articles and links and read them later. The application is developed and released as open source software and is avalible on your smart phone, tablet and desktop. Wallabag can be self-hosted for free, or used as a service for a monthly subscription.
ProtonMail
World's largest secure email service providing end-to-end encrypted email accounts. ProtonMail is based in Geneva, Switzerland and protected by Swiss privacy laws. The software is openly developed with fully open source code.
KeePassDroid
KeePassDroid is a port of the KeePass Password safe for the Android platform. With KeePassDroid password manager you can safetly and securely manage passwords for your mobile android device.