gulp-multi-bundle.js

var gulp       = require('gulp'),
    source     = require('vinyl-source-stream'),
    rename     = require('gulp-rename'),
    browserify = require('browserify'),
    es         = require('event-stream');

gulp.task('default', function() {
    // set entry files
    var files = [
        './app/entry-a.js',
        './app/entry-b.js'
    ];
    // map them to  streams
    var tasks = files.map(function(entry) {
        return browserify({ entries: [entry] })
            .bundle()
            .pipe(source(entry))
            .pipe(rename({
                extname: '.bundle.js'
            }))
            .pipe(gulp.dest('./dist'));
        });
    // merge
    return es.merge.apply(null, tasks);
});