Index: network_gui.c
===================================================================
--- network_gui.c	(revision 5963)
+++ network_gui.c	(working copy)
@@ -55,6 +55,7 @@
 static NetworkGameSorting _ng_sorting;
 
 static char _edit_str_buf[64];
+static char _chat_tab_completion_buf[lengthof(_edit_str_buf)];
 
 static void ShowNetworkStartServerWindow(void);
 static void ShowNetworkLobbyWindow(NetworkGameList *ngl);
@@ -1488,7 +1489,63 @@
 	}
 }
 
+static void ChatNickTabCompletion(Window *w)
+{
+	Textbuf *tb = &WP(w, querystr_d).text;
+	const NetworkClientInfo* ci;
+	int len, tb_len;
+	char *tb_buf;
+	bool second_scan = false;
 
+	tb_len = tb->length;
+	tb_buf = tb->buf;
+
+	for (ci = _network_client_info; ci != &_network_client_info[MAX_CLIENT_INFO]; ci++) {
+		/* Skip non-active items */
+		if (ci->client_index == NETWORK_EMPTY_INDEX) continue;
+
+		if (_chat_tab_completion_buf[0] != '\0') {
+			/* We are pressing TAB again on the same name, is there an other name
+			 *  that starts with this? */
+			if (!second_scan) {
+				/* Find the current match */
+				if (strlen(ci->client_name) == (uint)tb->length - 2 && strncmp(ci->client_name, tb->buf, tb->length - 2) == 0) second_scan = true;
+				continue;
+			}
+
+			/* Now any match we make on _chat_tab_completion_buf after this, is perfect */
+			tb_len = strlen(_chat_tab_completion_buf);
+			tb_buf = _chat_tab_completion_buf;
+		}
+
+		len = strlen(ci->client_name);
+		if (tb_len < len && strncasecmp(ci->client_name, tb_buf, tb_len) == 0) {
+			/* Save the data it was before completion */
+			if (!second_scan) snprintf(_chat_tab_completion_buf, lengthof(_chat_tab_completion_buf), "%s", tb_buf);
+
+			/* Change to the found nick */
+			snprintf(tb->buf, lengthof(_edit_str_buf), "%s: ", ci->client_name);
+
+			/* Update the textbuffer */
+			UpdateTextBufferSize(&WP(w, querystr_d).text);
+
+			SetWindowDirty(w);
+			return;
+		}
+	}
+
+	if (second_scan) {
+		/* We walked all posibilities, and the user presses tab again.. revert to original text */
+		strcpy(tb->buf, _chat_tab_completion_buf);
+		_chat_tab_completion_buf[0] = '\0';
+
+		/* Update the textbuffer */
+		UpdateTextBufferSize(&WP(w, querystr_d).text);
+
+		SetWindowDirty(w);
+	}
+}
+
 /* uses querystr_d WP macro */
 static void ChatWindowWndProc(Window *w, WindowEvent *e)
 {
@@ -1515,9 +1572,14 @@
 		break;
 
 	case WE_KEYPRESS:
-		switch (HandleEditBoxKey(w, &WP(w, querystr_d), 1, e, CS_ALPHANUMERAL)) {
-			case 1: /* Return */ SendChat(WP(w, querystr_d).text.buf); /* FALLTHROUGH */
-			case 2: /* Escape */ DeleteWindow(w); break;
+		if (e->keypress.keycode == WKC_TAB) {
+			ChatNickTabCompletion(w);
+		} else {
+			_chat_tab_completion_buf[0] = '\0';
+			switch (HandleEditBoxKey(w, &WP(w, querystr_d), 1, e, CS_ALPHANUMERAL)) {
+				case 1: /* Return */ SendChat(WP(w, querystr_d).text.buf); /* FALLTHROUGH */
+				case 2: /* Escape */ DeleteWindow(w); break;
+			}
 		}
 		break;
 
@@ -1555,6 +1617,7 @@
 	DeleteWindowById(WC_SEND_NETWORK_MSG, 0);
 
 	_edit_str_buf[0] = '\0';
+	_chat_tab_completion_buf[0] = '\0';
 
 	w = AllocateWindowDesc(&_chat_window_desc);