diff --git a/documentation/Clients.md b/documentation/Clients.md
index 380c423c0..10ab64ad4 100644
--- a/documentation/Clients.md
+++ b/documentation/Clients.md
@@ -1,6 +1,7 @@
 # Clients
 
 @subpage gtfpga
+@subpage opal
 
 Every server needs clients which they serve. In case of S2SS these clients are called _nodes_.
 
diff --git a/documentation/GTPGA.md b/documentation/GTPGA.md
deleted file mode 100644
index f3452b3d8..000000000
--- a/documentation/GTPGA.md
+++ /dev/null
@@ -1,3 +0,0 @@
-# GTFPGA {#gtfpga}
-
-Hallo :-)
diff --git a/documentation/Server.md b/documentation/Server.md
new file mode 100644
index 000000000..7864a4ea1
--- /dev/null
+++ b/documentation/Server.md
@@ -0,0 +1,3 @@
+# Server {#server}
+
+@todo Move documentation from Mainpage to Server.
diff --git a/documentation/clients/GTFPGA.md b/documentation/clients/GTFPGA.md
new file mode 100644
index 000000000..ae6999080
--- /dev/null
+++ b/documentation/clients/GTFPGA.md
@@ -0,0 +1,11 @@
+# GTFPGA {#gtfpga}
+
+The GTFPGA card is an extension card for simulator racks from RTDS.
+The manufacturer provides a VHDL module to exchange data via fiber optics between the GTFPGA and GPC cards.
+
+The GTFPGA card is based on the Xilinx ML507 evaluation board.
+This board consists of a Virtex 5 FPGA, Ethernet and Fiberoptic MACs and an integrated PowerPC core.
+
+The PowerPC core is used to forward values between RTDS and the S2SS server.
+
+@todo Add documentation for GTFPGA card.
diff --git a/documentation/clients/OPAL.md b/documentation/clients/OPAL.md
new file mode 100644
index 000000000..c1eae6226
--- /dev/null
+++ b/documentation/clients/OPAL.md
@@ -0,0 +1,3 @@
+# OPAL-RT {#opal}
+
+@todo Complete documentation for the OPAL-RT Simulink module.