[SalesForce] New button does not appear on the list view in Salesforce1

Peter is totally right, the concept of and "App" in S1 is a little different. Also, I would like to add a little bit more about a new metadata type that S1 introduced in this release ( I think Peter know about it too and he also recommended to me a good way to explain it :) ) , that we could consider the new view of "Apps".

If we make ourselves the question, what is having/ containing the App that we know at this moment? What we know, an app can contain different tabs , that are pointing to different objects for example ( and sometimes tab related with VF pages), and what has a tab when you click on it? a default list view. Then we could say that an App contain a list of tabs with default list views.

Well the new metadata type that S1 introduced is "Flexipage" , the flexipage will allow us to have diferent list views in only one page and also ( that the really nice part) have quick actions on it. Then this Flexipage , will be like a container where we will be able to put different list views, filtered list views or related to recent records, and quick global actions.

The Flexipage will appear like another tab in that picture and you can put it down or up ( using mobile administration).

To finish , I need to say that this metadata does not have a UI creation in this version of Salesforce, the new metadata is only possible to be create by deploying it into the org ( using ant commands or eclipse...) Once the Flexipage is deployed into the org you will be able to find it in : Create -- > tabs --> Flexipage Tab , and you will be able to configure the icon too.

I leave you here a code example of flexipage :

<?xml version="1.0" encoding="UTF-8"?>
 <FlexiPage xmlns="http://soap.sforce.com/2006/04/metadata">
    <flexiPageRegions>
        <componentInstances>
            <componentInstanceProperties>
                <name>entityName</name>
                <value>Account</value>
            </componentInstanceProperties>
            <componentInstanceProperties>
                <name>filterName</name>
                <value>MyAccounts</value>
            </componentInstanceProperties>
            <componentName>flexipage:filterListCard</componentName>
        </componentInstances>
        <componentInstances>
            <componentInstanceProperties>
                <name>entityName</name>
                <value>Contact</value>
            </componentInstanceProperties>
            <componentInstanceProperties>
                <name>filterName</name>
                <value>MyContacts</value>
            </componentInstanceProperties>
            <componentName>flexipage:filterListCard</componentName>
        </componentInstances>
        <componentInstances>
            <componentInstanceProperties>
                <name>entityNames</name>
                <value>MyCustomObject__c</value>
            </componentInstanceProperties>
            <componentName>flexipage:recentItems</componentName>
        </componentInstances>
        <name>main</name>
    </flexiPageRegions>
    <masterLabel>My new App</masterLabel>
    <quickActionList>
        <quickActionListItems>
            <quickActionName>flexiAction</quickActionName>
        </quickActionListItems>
    </quickActionList>
</FlexiPage>

I hope it is helpfull :)

Avoid using Pagereference methods in salesforce1 and usually i would prefer using @Remote action method to implement logic

Lets take a quick look with sample code below on how to achieve this

function actioninvoke(){
   if( (typeof sforce != 'undefined') && (sforce != null) ) {
   // Salesforce1 Remote Action method built in controller

   }
   else {
   //Action Function of normal App
   }
 }

Visualforce Code

 <apex:CommandButton value="Next" onclick="actioninvoke();" id="cmdNext" />

The advantages of remote action will be ability to callback and in callback we can use navigation specific function of salesforce1 like sforce.one

navigateToSObject(recordId,view)    //Navigates to an sObject record, specified by recordId.view is optional, and specifies the view within record home to select—chatter, related, or   detail.