KeePass is an open source password manager. Essentially, it provides a user-friendly GUI to store websites, logins and passwords. All of these are encrypted and stored inside a single file. You provide a encryption phrase (a key) to decrypt, access, modify and re-encrypt this file.
The advantage of KeePass is that it is free and thanks to it being open source, it has been ported to almost any platform or device you can think of. It only requires the single encrypted file to be available for reading and writing. For example, you can save this file on Dropbox and access it from any of your personal computers or your phone or tablet.
The disadvantage of KeePass is that its GUI may not look as polished as the other commercial password managers. This is especially true on Android.
Installing KeePass on Ubuntu is easy because it is available in the archives:
$ sudo apt install keepass2
After installation, you can access KeePass2 from the Dash.
There are many Android ports of KeePass. I'm currently using KeePassDroid. Its user interface is quite outdated, but it works with my encrypted file stored on Dropbox.