Hold space bar and press a key to launch/open something.

space-launcher.xml

<?xml version="1.0"?>

<!--
This is a Karabiner configuration file.

Hold space bar and press a key to launch/open something.
e.g.
space + ` to open home folder
space + 1 to open Dropbox folder
space + S to launch Safari
space + T to launch Terminal

For more info, https://pqrs.org/osx/karabiner/xml.html.en

The idea is from http://technicallysimple.com/screencasts/alfred-2-hotkeys/
-->

<!--
How To Configure
1. Karabiner -> Preferences -> Misc & Uninstall -> Open private.xml
2. Copy and paste the text below,
~~~
<?xml version="1.0"?>
<root>
  <include path="path_to_current_file" />
</root>
~~~
3. Replace path_to_current_file. {{ ENV_HOME }} could be used as home path.
4. Karabiner -> Preferences -> Change Key -> Reload XML
5. Select Space Launcher
6. Optionally, Karabiner -> Parameters -> Key Overlaid Modifier -> Initial Modifier Wait, increase this value (e.g. 120) if your typing speed is too fast.
-->

<root>

<!---- apps ---->

  <!-- CotEditor -->
  <vkopenurldef>
    <name>KeyCode::VK_OPEN_URL_APP_CotEditor</name>
    <url type="file">/Applications/CotEditor.app</url>
  </vkopenurldef>
  <!-- EuDic -->
  <vkopenurldef>
    <name>KeyCode::VK_OPEN_URL_APP_EuDic</name>
    <url type="file">/Applications/Eudb_en.app</url>
  </vkopenurldef>
  <!-- LaunchBar -->
  <vkopenurldef>
    <name>KeyCode::VK_OPEN_URL_APP_LaunchBar</name>
    <url type="file">/Applications/LaunchBar.app</url>
  </vkopenurldef>
  <!-- LDOCE5 Viewer -->
  <vkopenurldef>
    <name>KeyCode::VK_OPEN_URL_APP_LDOCE5Viewer</name>
    <url type="file">/Applications/LDOCE5 Viewer.app</url>
  </vkopenurldef>
  <!-- MacVim -->
  <vkopenurldef>
    <name>KeyCode::VK_OPEN_URL_APP_MacVim</name>
    <url type="file">/Applications/MacVim.app</url>
  </vkopenurldef>
  <!-- nvALT -->
  <vkopenurldef>
    <name>KeyCode::VK_OPEN_URL_APP_nvALT</name>
    <url type="file">/Applications/nvALT.app</url>
  </vkopenurldef>
  <!-- Preview -->
  <vkopenurldef>
    <name>KeyCode::VK_OPEN_URL_APP_Preview</name>
    <url type="file">/Applications/Preview.app</url>
  </vkopenurldef>
  <!-- Simplenote -->
  <vkopenurldef>
    <name>KeyCode::VK_OPEN_URL_APP_Simplenote</name>
    <url type="file">/Applications/Simplenote.app</url>
  </vkopenurldef>
  <!-- Tower -->
  <vkopenurldef>
    <name>KeyCode::VK_OPEN_URL_APP_Tower</name>
    <url type="file">/Applications/Tower.app</url>
  </vkopenurldef>

<!---- folders ---->

  <!-- Dropbox -->
  <vkopenurldef>
    <name>KeyCode::VK_OPEN_URL_FILE_Dropbox</name>
    <url type="file">{{ ENV_HOME }}/Dropbox</url>
  </vkopenurldef>
  <!-- Documents -->
  <vkopenurldef>
    <name>KeyCode::VK_OPEN_URL_FILE_Documents</name>
    <url type="file">{{ ENV_HOME }}/Documents</url>
  </vkopenurldef>
  <!-- Developer -->
  <vkopenurldef>
    <name>KeyCode::VK_OPEN_URL_FILE_Developer</name>
    <url type="file">{{ ENV_HOME }}/Developer</url>
  </vkopenurldef>
  <!-- Library -->
  <vkopenurldef>
    <name>KeyCode::VK_OPEN_URL_FILE_Library</name>
    <url type="file">{{ ENV_HOME }}/Library</url>
  </vkopenurldef>
  <!-- Downloads -->
  <vkopenurldef>
    <name>KeyCode::VK_OPEN_URL_FILE_Downloads</name>
    <url type="file">{{ ENV_HOME }}/Downloads</url>
  </vkopenurldef>
  
<!---- URL ---->

  <!-- System Preferences in LaunchBar -->
  <vkopenurldef>
    <name>KeyCode::VK_OPEN_URL_SystemPreferencesInLaunchBar</name>
    <url>x-launchbar:select?abbreviation=systempreferences</url>
  </vkopenurldef>

<!---- keys ---->
  
  <modifierdef>SPACE_LAUNCHER</modifierdef>
  <item>
    <name>Space Launcher</name>
    <appendix>Space + Key(s) to launch applications / open folders / run scripts</appendix>
    <identifier>name.guoc.space-launcher</identifier>
    <!-- Change the space key to my launcher key. -->
    <autogen>
      __KeyOverlaidModifier__
      KeyCode::SPACE,
      KeyCode::VK_MODIFIER_SPACE_LAUNCHER,
      KeyCode::SPACE
    </autogen>
    <modifier_not>
        ModifierFlag::COMMAND_L, ModifierFlag::COMMAND_R,
        ModifierFlag::OPTION_L,  ModifierFlag::OPTION_R,
        ModifierFlag::SHIFT_L,   ModifierFlag::SHIFT_R,
        ModifierFlag::CONTROL_L,   ModifierFlag::CONTROL_R,
        ModifierFlag::FN,
    </modifier_not>
    <!-- space launcher key settings -->
    <autogen>
      __KeyToKey__
      KeyCode::BACKQUOTE, ModifierFlag::SPACE_LAUNCHER,
      KeyCode:: VK_OPEN_URL_FILE_Home,
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::KEY_1, ModifierFlag::SPACE_LAUNCHER,
      KeyCode:: VK_OPEN_URL_FILE_Dropbox,
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::KEY_2, ModifierFlag::SPACE_LAUNCHER,
      KeyCode:: VK_OPEN_URL_FILE_Documents,
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::KEY_3, ModifierFlag::SPACE_LAUNCHER,
      KeyCode:: VK_OPEN_URL_FILE_Developer,
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::KEY_4, ModifierFlag::SPACE_LAUNCHER,
      KeyCode:: VK_OPEN_URL_FILE_Downloads,
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::KEY_0, ModifierFlag::SPACE_LAUNCHER,
      KeyCode:: VK_OPEN_URL_FILE_Library,
    </autogen>

    <autogen>
      __KeyToKey__
      KeyCode::C, ModifierFlag::SPACE_LAUNCHER,
      KeyCode:: VK_OPEN_URL_APP_CotEditor,
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::D, ModifierFlag::SPACE_LAUNCHER,
      KeyCode:: VK_OPEN_URL_APP_Dictionary,
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::E, ModifierFlag::SPACE_LAUNCHER,
      KeyCode:: VK_OPEN_URL_APP_EuDic,
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::F, ModifierFlag::SPACE_LAUNCHER,
      KeyCode:: VK_OPEN_URL_APP_Finder,
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::G, ModifierFlag::SPACE_LAUNCHER,
      KeyCode:: VK_OPEN_URL_APP_Tower,
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::K, ModifierFlag::SPACE_LAUNCHER,
      KeyCode:: VK_OPEN_URL_APP_Karabiner,
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::L, ModifierFlag::SPACE_LAUNCHER,
      KeyCode:: VK_OPEN_URL_APP_LaunchBar,
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::N, ModifierFlag::SPACE_LAUNCHER,
      KeyCode:: VK_OPEN_URL_APP_nvALT,
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::O, ModifierFlag::SPACE_LAUNCHER,
      KeyCode:: VK_OPEN_URL_APP_LDOCE5Viewer,
    </autogen>
    <! -- OS X System Preference Links (URL Schemes) https://macosxautomation.com/system-prefs-links.html -->
    <autogen>
      __HoldingKeyToKey__
      KeyCode::P, ModifierFlag::SPACE_LAUNCHER,
      <!-- short press -->
      @begin
      KeyCode:: VK_OPEN_URL_APP_System_Preferences,
      @end
      <!-- hold -->
      @begin
      KeyCode::VK_OPEN_URL_SystemPreferencesInLaunchBar,
      @end
      <!-- The KEYTOKEY_AFTER_KEYUP option can not be set for only one case above, 
      CURSOR_LEFT followed by CURSOR_RIGHT is a workaround. -->
      Option::KEYTOKEY_AFTER_KEYUP, KeyCode::CURSOR_LEFT, KeyCode::CURSOR_RIGHT,
      Option::NOREPEAT,
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::R, ModifierFlag::SPACE_LAUNCHER,
      KeyCode::VK_OPEN_URL_APP_Preview,
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::S, ModifierFlag::SPACE_LAUNCHER,
      KeyCode::VK_OPEN_URL_APP_Safari,
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::T, ModifierFlag::SPACE_LAUNCHER,
      KeyCode::VK_OPEN_URL_APP_Terminal,
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::V, ModifierFlag::SPACE_LAUNCHER,
      KeyCode::VK_OPEN_URL_APP_MacVim,
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::X, ModifierFlag::SPACE_LAUNCHER,
      KeyCode:: VK_OPEN_URL_APP_Xcode,
    </autogen>

    <!-- Drop all events which are not modified in above. -->
    <autogen>
      __DropAllKeys__
      ModifierFlag::SPACE_LAUNCHER,

      Option::DROPALLKEYS_DROP_KEY,
      Option::DROPALLKEYS_DROP_CONSUMERKEY,
      Option::DROPALLKEYS_DROP_POINTINGBUTTON,
    </autogen>
  </item>
</root>

Karabiner is not compatible with macOS Sierra. I've changed to SpaceLauncher to use spacebar as a better "hyper" key.