I want software to slow down my typing and increase my accuracy
You can use Karabiner to play a sound when you press delete. For example save this file as ~/Library/Application Support/Karabiner/private.xml:

&lt;?xml version="1.0"?&gt;
&lt;root&gt;
  &lt;vkopenurldef&gt;
    &lt;name&gt;KeyCode::VK_OPEN_URL_SHELL_BEEP&lt;/name&gt;
    &lt;url type="shell"&gt;afplay /System/Library/PrivateFrameworks/ScreenReader.framework/Versions/A/Resources/Sounds/BrailleChordFailed.aiff&lt;/url&gt;
  &lt;/vkopenurldef&gt;
  &lt;item&gt;
    &lt;name&gt;custom&lt;/name&gt;
    &lt;identifier&gt;custom&lt;/identifier&gt;
    &lt;autogen&gt;__KeyToKey__ KeyCode::DELETE, ModifierFlag::NONE, KeyCode::DELETE, KeyCode::VK_OPEN_URL_SHELL_BEEP&lt;/autogen&gt;
  &lt;/item&gt;
&lt;/root&gt;


Then open the Karabiner application, press the ReloadXML button and enable the setting.

You could also use Master Key or TypeRacer to practice typing pieces of plain text.