<apex:page standardController="Dev_Request__c" extensions="tableDevRequest_edit">
    <apex:form >
        <apex:pageblock mode="inlineEdit">
            <apex:pageMessages />
            <apex:pageBlockButtons >
            <!--<apex:commandButton value="Save" action="{!saveTable}" id="saveButton" rendered="{!editTable==true}" immediate="true"/>-->
            <apex:commandButton value="Save" action="{!saveTable}" id="saveButton" immediate="true"/>
            <apex:commandButton id="cancelButton" value="Cancel"/>
            </apex:pageBlockButtons>

             <apex:pageblocktable value="{!lstDevRequest_edit}"  var="item">
                    <apex:column headerValue="Dev Request Name"><apex:actionRegion ><apex:outputField value="{!item.Name}"><apex:inlineEditSupport event="ondblClick" showOnEdit="saveButton,cancelButton" /></apex:outputField></apex:actionRegion></apex:column>
                    <apex:column headerValue="Id"><apex:outputField value="{!item.Id}"/></apex:column>
                    <apex:column headerValue="Status"><apex:inputField value="{!item.Status__c}"/></apex:column>
                    <apex:column headerValue="Start Date"><apex:inputField value="{!item.Start_Date__c}"/></apex:column>
                    <apex:column headerValue="Due Date QA"><apex:inputField value="{!item.Due_Date_QA__c}"/></apex:column>
                    <apex:column headerValue="Estimated Hours"><apex:inputField value="{!item.Estimated_Hours__c}"/></apex:column>
                    <apex:column headerValue="Assignee"><apex:inputField value="{!item.Assignee__c}"/></apex:column>
                    <apex:column headerValue="Overview"><apex:inputField value="{!item.Overview__c}"/></apex:column>
             </apex:pageblocktable>

        </apex:pageblock>
    </apex:form>

public with sharing class tableDevRequest_edit {

   public List<Dev_Request__c> lstDevRequest_edit {get;set;}

    public tableDevRequest_edit(ApexPages.StandardController controller) {
        lstDevRequest_edit = [Select Id, Name, Assignee__c, Assignee__r.Name, Start_Date__c, Due_Date_QA__c, Estimated_Hours__c, Estimated_Completion_Date__c, Status__c, Overview__c from Dev_Request__c];
    }

    public PageReference saveTable() {
        try {
            update lstDevRequest_edit;
        }
        catch(Exception e){
            System.debug('Exception occurred '+String.valueOf(e));
        }
        return NULL;
    }
}