gistfile1.js

var waiter = new Waiter
var onlineUsers = waiter(function(done) { // done takes two arguments: (error, value)
    //  ... blah blah blah ...
    done(err,value)
    // ... blah ...
}
var latestPosts = waiter(function(done) {
    // ... blah ... 
    // many async functions will accept 'done' as is 
    // ... 
}

waiter.waitForAll(function(errors) {
    if (errors) { // an array of all errors
        // onlineUsers.error latestPosts.error have errors
    }
    // onlineUsers.value and latestPosts.value have values
})

waiter.waitFor(1, function(errors) { ... }) // waits for a single result

waiter.waitForAll(function(errors) { ... }, 2000) // optional timeout (sets errors for any requests that don't respond in time)

waiter.waitFor(2, function(errors) { ... }, 2000) // count and timeout


// Oh and here's the code for waiter:

module.exports = function() {
    var errors,
        values = {},
        expecting = [],
        count = 0,
        max = 0,
        waitCount,
        waitCallback,
        timeouter

    function completed(result, error, value) {
        result.error = error
        result.value = value
        expecting = expecting.filter(function(o) { return o !== result })
        if (error) {
            (errors||(errors=[])).push(error)
        }
        count++
        if (waitCount == count) {
            waitCallback(errors)
            if (timeouter) {
                clearTimeout(timeouter)
                timeouter = null
            }
        }
    }

    function WaiterInstance(callback) {
        max++
        var result = {}
        expecting.push(result)
        callback(function (error, value) {
            completed(result,error,value)
        })
        return result
    }
    WaiterInstance.waitFor = function(n, callback, timeout) {
        if (count >= n) {
            callback(errors,values)
        } else {
            waitCount = n
            waitCallback = callback
            if (timeout) {
                timeouter = setTimeout(function() {
                    var error = new Error("Timeout after "+timeout+" ms")
                    expecting.forEach(function (result) {
                        completed(result, error)
                    })
                }, timeout)
            }
        }
        return this
    }
    WaiterInstance.waitForAll = function(callback, timeout) {
        return this.waitFor(max, callback, timeout)
    }
    return WaiterInstance
}