oulipo

Some Oulipian constraints:

S+7, sometimes called N+7
Replace every noun in a text with the noun seven entries after it in a dictionary. For example, "Call me Ishmael. Some years ago..." (from Moby-Dick) becomes "Call me islander. Some yeggs ago...". Results will vary depending upon the dictionary used. This technique can also be performed on other lexical classes, such as verbs.

Snowball
A poem in which each line is a single word, and each successive word is one letter longer.

Lipogram
Writing that excludes one or more letters. The previous sentence is a lipogram in B, F, H, J, K, Q, V, Y, and Z (it does not contain any of those letters).

Prisoner's constraint, also called Macao constraint
A type of lipogram that omits letters with ascenders and descenders (b, d, f, g, h, j, k, l, p, q, t, and y).

Palindromes
Sonnets and other poems constructed using palindromic techniques.

Univocalism
A poem using only one vowel, although the vowel may be used in any of its aural forms. For example, "born" and "cot" could both be used in a univocalism, unlike "sew" and "beau".