1. XCVB
    XCVB, an eXtensible Component Verifier and Builder for Lisp is an attempt to replace asdf
  2. xelf
    Xelf is a simple 2-D game engine for Common Lisp
  3. xgboost
    Common Lisp interface to XGBoost
  4. xhtmlgen
    xhtmlgen is an XHTML generator
  5. XHTMΛ
    XHTMΛ is yet another (X)HTML/XML manipulation library You can find it at common-lisp.net/project/xhtmlambda
  6. xindy
    xindy is an index processor that can be used to generate book-like indexes for arbitrary document preparation systems
  7. XIT
    A graphics toolkit from the University of Stuttgart which provides an object-based interface to the X11 window system, based on CLX and CLUE
  8. XL-Wiki
    XL-Wiki is a fork of CL-Wiki that aims to allow applications to modify and extend its functionality in interesting ways
  9. xlunit
    XLUnit is a Test Framework based on XPTest and JUnit
  10. XML
    The eXtensible Markup Language