Constructed languages are languages invented by individuals rather than naturally developed, for purposes ranging from facilitating communication between speakers of different languages (the most famous being Esperanto) to simply serving as works of art.

my conlangs

• Xõópríf is a conlang spoken by people who have no tongue, teeth, or nose. (It is very, very far from being complete.)

other people's conlangs

• In 1921, Jacob Linzbach invented a writing system based on mathematical notation and published his work in a little-known book written in the now-obsolete international auxiliary language Occidental. Here is a transcription and translation of the book about the writing system called Transcendental Algebra.
• toki pona is a conlang made by Sonja Lang. I have produced a toki pona translation of the Telegram desktop application, which is ~50% complete. I also made a reference pdf based on jan Pije's lessons, which I fondly remember as how I first learned toki pona. Unfortunately, I can't locate an extant source of that specific dictionary, even archived. The content is in the public domain, but it would still be nice to find the original, so if you do, let me know!