A very basic framework for creating front-end forms for WordPress.

functions.php

<?php 
// a framework to handle frontend form submission
// written by Arūnas Liuiza | tinyStudio | wp.tribuna.lt
// Usage: use [tiny_form1] shortcode or get_tiny_form1()/the_tiny_form1() template tags
// Arguments: one (optional) argument 'redirect': pass url where to redirect after successful login (default: false);
 
// Localization: replace 'theme' with your text domain string.
 
// ======= FORM 1 =====>
 
// return form #1
// usage: $result = get_tiny_form1();
function get_tiny_form1($redirect=false) {
  $return = "<form action=\"\" method=\"post\" class=\"tiny_form tiny_form1\">\r\n";
// add as many inputs, selects, textareas as needed
  $return .= "  <p>
    <label for=\"tiny_password\">".__('Password','theme')."</label>
    <input type=\"password\" id=\"tiny_password\" name=\"password\"/>
  </p>\r\n";

// where to redirect on success
  if ($redirect)
    $return .= "  <input type=\"hidden\" name=\"redirect\" value=\"{$redirect}\">\r\n";

  $return .= "  <input type=\"hidden\" name=\"tiny_action\" value=\"form1\">\r\n";
  $return .= "  <button type=\"submit\">".__('Login','theme')."</button>\r\n";
  $return .= "</form>\r\n";
  return $return;
}
// print form #1
/* usage: <?php the_tiny_form1(); ?> */
function the_tiny_form1($redirect=false) {
  echo get_tiny_form1($redirect);
}
// shortcode for form #1
// usage: [tiny_form1] in post/page content
add_shortcode('tiny_form1','tiny_form1_shortcode');
function tiny_form1_shortcode ($atts,$content=false) {
  $atts = shortcode_atts(array(
    'redirect' => false
  ), $atts);
  return get_tiny_form1($atts['redirect']);
}

// <============== FORM 1


// ======= FORM 2 =====>
 
// return form #2
// usage: $result = get_tiny_form2();
function get_tiny_form2($redirect=false) {
  $return = "<form action=\"\" method=\"post\" class=\"tiny_form tiny_form2\">\r\n";
// add as many inputs, selects, textareas as needed
  $return .= "  <p>
    <label for=\"tiny_password\">".__('Password','theme')."</label>
    <input type=\"password\" id=\"tiny_password\" name=\"password\"/>
  </p>\r\n";

// where to redirect on success
  if ($redirect)
    $return .= "  <input type=\"hidden\" name=\"redirect\" value=\"{$redirect}\">\r\n";

// which action handler to use
  $return .= "  <input type=\"hidden\" name=\"tiny_action\" value=\"form2\">\r\n";

  $return .= "  <button type=\"submit\">".__('Login','theme')."</button>\r\n";
  $return .= "</form>\r\n";
  return $return;
}
// print form #1
/* usage: <?php the_tiny_form2(); ?> */
function the_tiny_form2($redirect=false) {
  echo get_tiny_form2($redirect);
}
// shortcode for form #1
// usage: [tiny_form2] in post/page content
add_shortcode('tiny_form2','tiny_form2_shortcode');
function tiny_form2_shortcode ($atts,$content=false) {
  $atts = shortcode_atts(array(
    'redirect' => false
  ), $atts);
  return get_tiny_form2($atts['redirect']);
}

// <============== FORM 2

// ============ FORM SUBMISSION HANDLER
add_action('init','tiny_handle');
function tiny_handle() {
  if (isset($_POST['tiny_action'])) {
    switch ($_POST['tiny_action']) {
      case 'form1':
          // handle form #1 submission
          // write data to db or perform other actions

          // if actions vere successful
          $success = true;
        break;
      case 'form2':
          // handle form #2 submission
          // write data to db or perform other actions

          // if actions vere successful
          $success = true;
        break;
      // add more cases if you have more forms
    }

    // if redirect is set and action was successful
    if (isset($_POST['redirect']) && $_POST['redirect'] && $success) {
      wp_redirect($_POST['redirect']);
    }      
  }
}

?>