In one of my requirements, we had to use the Rich Text Box in the application page. In this blog, I will list you the steps to bring the richtextbox in the application page.
To implement the RichBox in SharePoint 2013,
a. Add the mentioned below Import Directive,
<%@Register Tagprefix="SharePoint" Namespace="Microsoft.SharePoint.WebControls" Assembly="Microsoft.SharePoint, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>
b. Add the mentioned below Control in the Application page,
<SharePoint:InputFormTextBox ID="rftmytext" RichText="true" RichTextMode="FullHtml" runat="server"TextMode="MultiLine"Rows="5">
</SharePoint:InputFormTextBox>