diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6e4cc001..30b2d0ae 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -93,6 +93,7 @@ add_subdirectory(xo-statistics)
 add_subdirectory(xo-distribution)
 add_subdirectory(xo-pydistribution)
 add_subdirectory(xo-simulator)
+add_subdirectory(xo-pysimulator)
 #add_subdirectory(xo-process)
 #
 add_subdirectory(xo-expression)
@@ -102,7 +103,6 @@ add_subdirectory(xo-reader)
 add_subdirectory(xo-jit)
 add_subdirectory(xo-pyjit)
 #
-#add_subdirectory(xo-pysimulator)
 #add_subdirectory(xo-process)
 #add_subdirectory(xo-pyprocess)
 #add_subdirectory(xo-kalmanfilter)
diff --git a/default.nix b/default.nix
index a255e23b..1f99d5e9 100644
--- a/default.nix
+++ b/default.nix
@@ -66,6 +66,7 @@ let
           xo-distribution   = self.callPackage pkgs/xo-distribution.nix   {};
           xo-pydistribution = self.callPackage pkgs/xo-pydistribution.nix {};
           xo-simulator      = self.callPackage pkgs/xo-simulator.nix      {};
+          xo-pysimulator    = self.callPackage pkgs/xo-pysimulator.nix    {};
 #          xo-process        = self.callPackage pkgs/xo-process.nix        {};
 #
           xo-expression     = self.callPackage pkgs/xo-expression.nix     {};
diff --git a/pkgs/xo-pysimulator.nix b/pkgs/xo-pysimulator.nix
new file mode 100644
index 00000000..02c21d3f
--- /dev/null
+++ b/pkgs/xo-pysimulator.nix
@@ -0,0 +1,59 @@
+{
+  # nixpkgs dependencies
+  stdenv, cmake, catch2, # ... other deps here
+
+#  python3Packages,
+
+  # xo dependencies
+  xo-cmake,
+
+  xo-simulator,
+  #xo-refcnt,
+  #xo-pyutil,
+  #xo-reflect,
+
+  xo-pyreactor,
+
+  # args
+
+  #   attrset for fetching source code.
+  #    { type, owner, repo, ref }
+  #
+  #   e.g. type="github", owner="rconybea", repo="cmake-examples", ref="ex1b"
+  #
+  #   see [[../flake.nix]]
+  #
+  #cmake-examples-ex1-path
+
+  # someconfigurationoption ? false
+} :
+
+stdenv.mkDerivation (finalattrs:
+  {
+    name = "xo-pysimulator";
+    version = "1.0";
+
+    outputs = [
+      "out"
+    ];
+
+    src = ../xo-pysimulator;
+
+    cmakeFlags = ["-DCMAKE_MODULE_PATH=${xo-cmake}/share/cmake"];
+    doCheck = true;
+
+    propagatedBuildInputs = [
+#      xo-refcnt
+      xo-pyreactor
+      xo-simulator
+#      xo-reflect
+    ];
+
+    nativeBuildInputs = [
+      cmake
+#      catch2
+      xo-cmake
+#      python3Packages.pybind11
+    ];
+
+  })
diff --git a/pkgs/xo-userenv.nix b/pkgs/xo-userenv.nix
index aba839a4..2f4a02bc 100644
--- a/pkgs/xo-userenv.nix
+++ b/pkgs/xo-userenv.nix
@@ -51,8 +51,8 @@
   xo-distribution,
   xo-pydistribution,
   xo-simulator,
+  xo-pysimulator,
 #  xo-process,
-  #  xo-pysimulator,
   #xo-pyprocess,
   #xo-kalmanfilter,
   #  xo-pykalmanfilter,
@@ -99,6 +99,7 @@ buildEnv {
             xo-distribution
             xo-pydistribution
             xo-simulator
+            xo-pysimulator
 #            xo-process
 #
             xo-expression
@@ -107,7 +108,6 @@ buildEnv {
             xo-reader
             xo-jit
             xo-pyjit
-#            xo-pysimulator
 #            xo-pyprocess
 #            xo-kalmanfilter
 #            xo-pykalmanfilter