The Lepcha script was developed either by prince Phyagdor Namgyal or by the scholar Thikúng Men Salóng sometime around 1700 AD. Although it was pretty clearly derived from Tibetan, which is written left-to-right, early Lepcha was written vertically, probably from Chinese influence.
To write the language vertically, they rotated everything 90 degrees. After not very much time, they switched to left-to-right like Tibetan, but declined to change the orientation of the glyphs. The the Lepcha glyphs look very similar to Tibetan glyphs, but rotated 90 degrees.
Note that the Lepcha glyphs are rotated 90 degrees counter-clockwise, while you would think that going from left-to-right to top-to-bottom, they would rotate them by 90 degrees clockwise. I have no explanation for that: I don’t know if they wrote bottom-to-top or did some strange gymnastics.
In Lepcha, there are some syllables that end with a consonant, meaning a vowel needs to be killed. Unlike Tibetan, which kills vowels by using consonant conjuncts, Lepcha uses diacritics to mark final consonants. (My sources say that this is due to the funky double-rotation that happened, but don’t explain how.) The glyph adorning this post is made up of two pieces: the “fla” on the bottom, and the twirly little “n” diacritic on the top.