Toki Pona is a conlang created by Canadian linguist Sonja Lang in 2001. With only 120 official words, the language is inspired by Taoism, and designed to get rid of unnecessary complex thoughts. In a way, it can be seen as a tool for mental health and mental hygiene.
There is no gender, no plural, no tense. Words can generally be used as nouns, adjectives or verbs. Unlike logical languages like Lojban, Toki Pona relies heavily on context and is highly ambiguous. Most words have a wide range of meaning, yet the minimalistic grammar makes its easy to learn and use.
Toki Pona uses only fourteen letters and is usually written with latin characters, but it also allows different scripts, such as sitelen pona, where each word is a simple glyph, or sitelen sitelen, a non-linear calligraphic system relying on complex Mayan-like blocks.
Many online resources are available to learn Toki Pona. Urandom's course is a great start. However, while reading the official book is not mandatory, it is highly recommended to get a true understanding of what the language is about.
Several of my projects involve Toki Pona, including musi lipu, pimeja, unpa pona, music, drawings, and more recently, ma kasi suno. For anyone interested in learning the language, I maintain a learning resources thread.
There's an endless war between "pu-rists", the people who use only the 120 words from the official book, also known as "Pu", and others, who enjoy inventing new words every now and them.
In my opinion, new words defeat the purpose of the language. While a few of them might actually be justified for important concepts, such as "tonsi", which refers to non-binary persons, most additions are superfluous.
The interest of Toki Pona is to embrace its minimalism: you have to think with a limited vocabulary, and twist your mind around the words it lacks to reach simpler or smarter ways of expressing your thoughts. Poetry, unknown feelings and introspection may arise.
While inventing new words can be fun, I think it also misses the point. Yes, a living language does evolve, but Toki Pona is meant to simplify your way of thinking, not to complexify it to suit your mindset.
I'd go as far as saying that some official words are useless, such as "mu", or even "pu", or redundant, like "suno" and "mun", and could be replaced with words bearing broader meanings.
I guess I'll end up making my own conlang at some point...