вот полный перечень, а почему? это сложилось со временем, почитать о них можно в нете.
gulp = require('gulp'),
sass = require('gulp-ruby-sass'),
autoPrefixer = require('gulp-autoprefixer'),
cleanCSS = require('gulp-clean-css'),
uglify = require('gulp-uglify'),
minifyHTML = require('gulp-minify-html'),
imageMin = require('gulp-imagemin'),
pngquant = require('imagemin-pngquant'),
jsHint = require('gulp-jshint'),
concat = require('gulp-concat'),
cache = require('gulp-cache'),
del = require('del'),
gulpFilter = require('gulp-filter'),
mainBowerFiles = require('main-bower-files'),
connect = require('gulp-connect'),
gulpIf = require('gulp-if'),
util = require('gulp-util'),
plumber = require('gulp-plumber'),
rigger = require('gulp-rigger'),
spritesmith = require('gulp.spritesmith'),
size = require('gulp-size'),
opn = require('opn');
