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If you worry about security, Gliph might be a great app for you. You create an account by claiming a Gliph, and then you can send encrypted text messages and cloak your email when using it on sites that you don't trust, although this feature only works under certain conditions on Android. You can even delete messages that you didn't mean to send to other users, not only on your device, but on theirs, too.
Platform: iOS (iPhone)
If you want to chat to people around you, but also want to be private or take control with an alter ego, Pick.ee might be for you. It lets you choose whether you want to be visible or invisible, and decide what fields you want to fill out about yourself and embellish to your heart's content. If you're looking for a particular type of person, you can put filters on to only show that kind of person.