diff --git a/src/engine/engine.cpp b/src/engine/engine.cpp
index 14577b40e..1c5d4dd2e 100644
--- a/src/engine/engine.cpp
+++ b/src/engine/engine.cpp
@@ -414,6 +414,7 @@ void DivEngine::runExportThread() {
   }
 }
 
+// TODO: properly export ExtCh songs in per-channel mode
 bool DivEngine::saveAudio(const char* path, int loops, DivAudioExportModes mode) {
   exportPath=path;
   exportMode=mode;
diff --git a/src/engine/waveSynth.cpp b/src/engine/waveSynth.cpp
index 4d776ba4c..e38ee228e 100644
--- a/src/engine/waveSynth.cpp
+++ b/src/engine/waveSynth.cpp
@@ -2,6 +2,10 @@
 #include "engine.h"
 #include "instrument.h"
 
+// TODO:
+// - add missing license header
+// - implement waveSynth on Amiga and N163
+
 bool DivWaveSynth::activeChanged() {
   if (activeChangedB) {
     activeChangedB=false;
diff --git a/src/gui/editControls.cpp b/src/gui/editControls.cpp
index 5e8d72574..8d9480242 100644
--- a/src/gui/editControls.cpp
+++ b/src/gui/editControls.cpp
@@ -20,6 +20,9 @@
 #include "gui.h"
 #include "IconsFontAwesome4.h"
 
+// TODO:
+// - "play from start" button/action
+// - fix behavior of play buttons
 void FurnaceGUI::drawEditControls() {
   if (nextWindow==GUI_WINDOW_EDIT_CONTROLS) {
     editControlsOpen=true;
diff --git a/src/gui/gui.h b/src/gui/gui.h
index 7cc66c847..53b2f1715 100644
--- a/src/gui/gui.h
+++ b/src/gui/gui.h
@@ -46,6 +46,9 @@
 
 #define BIND_FOR(x) getKeyName(actionKeys[x],true).c_str()
 
+// TODO:
+// - add colors for FM envelope and waveform
+// - maybe add "alternate" color for FM modulators/carriers (a bit difficult)
 enum FurnaceGUIColors {
   GUI_COLOR_BACKGROUND=0,
   GUI_COLOR_FRAME_BACKGROUND,
diff --git a/src/gui/insEdit.cpp b/src/gui/insEdit.cpp
index 3e1416128..f53db474c 100644
--- a/src/gui/insEdit.cpp
+++ b/src/gui/insEdit.cpp
@@ -1253,6 +1253,8 @@ if (ImGui::BeginTable("MacroSpace",2)) { \
 #define CENTER_VSLIDER \
   ImGui::SetCursorPosX(ImGui::GetCursorPosX()+0.5f*ImGui::GetContentRegionAvail().x-10.0f*dpiScale);
 
+// TODO:
+// - add right click line draw in macro editor
 void FurnaceGUI::drawInsEdit() {
   if (nextWindow==GUI_WINDOW_INS_EDIT) {
     insEditOpen=true;
diff --git a/src/gui/osc.cpp b/src/gui/osc.cpp
index c0ce978cf..e43dee1e0 100644
--- a/src/gui/osc.cpp
+++ b/src/gui/osc.cpp
@@ -22,6 +22,10 @@
 #include <imgui.h>
 #include <math.h>
 
+// TODO:
+// - potentially move oscilloscope seek position to the end, and read the last samples
+//   - this allows for setting up the window size
+// - reduce initial latency (it's too high)
 void FurnaceGUI::readOsc() {
   int writePos=e->oscWritePos;
   int readPos=e->oscReadPos;
@@ -65,6 +69,9 @@ void FurnaceGUI::readOsc() {
   e->oscReadPos=readPos;
 }
 
+// TODO:
+// - draw reference level
+// - draw guidelines
 void FurnaceGUI::drawOsc() {
   if (nextWindow==GUI_WINDOW_OSCILLOSCOPE) {
     oscOpen=true;
diff --git a/src/gui/pattern.cpp b/src/gui/pattern.cpp
index 0decef970..de0e5a61f 100644
--- a/src/gui/pattern.cpp
+++ b/src/gui/pattern.cpp
@@ -408,6 +408,7 @@ void FurnaceGUI::drawPattern() {
     patWindowSize=ImGui::GetWindowSize();
     //char id[32];
     ImGui::PushFont(patFont);
+    // TODO: separate GUI curOrder from engine curOrder
     int ord=e->isPlaying()?oldOrder:e->getOrder();
     oldOrder=e->getOrder();
     int chans=e->getTotalChannelCount();
diff --git a/src/gui/piano.cpp b/src/gui/piano.cpp
index d3a3d35ef..aa18996f3 100644
--- a/src/gui/piano.cpp
+++ b/src/gui/piano.cpp
@@ -20,6 +20,7 @@
 #include "gui.h"
 #include "guiConst.h"
 
+// TODO: actually implement a piano!
 void FurnaceGUI::drawPiano() {
   if (nextWindow==GUI_WINDOW_PIANO) {
     pianoOpen=true;
diff --git a/src/gui/sampleEdit.cpp b/src/gui/sampleEdit.cpp
index 04af4cab3..34cb23d5f 100644
--- a/src/gui/sampleEdit.cpp
+++ b/src/gui/sampleEdit.cpp
@@ -28,6 +28,12 @@
 #include "sampleUtil.h"
 #include "util.h"
 
+// TODO:
+// - resample should change C-4 note
+// - clicking on waveform should give this window focus
+// - add "create instrument using this sample" option
+// - .dmc loading
+// - duplicate sample
 void FurnaceGUI::drawSampleEdit() {
   if (nextWindow==GUI_WINDOW_SAMPLE_EDIT) {
     sampleEditOpen=true;
diff --git a/src/gui/settings.cpp b/src/gui/settings.cpp
index 87b798572..d8070dc65 100644
--- a/src/gui/settings.cpp
+++ b/src/gui/settings.cpp
@@ -198,6 +198,10 @@ struct MappedInput {
     scan(s), val(v) {}
 };
 
+// TODO:
+// - add metronome volume setting
+// - maybe add metronome sound setting
+// - add a "close" button to this window
 void FurnaceGUI::drawSettings() {
   if (nextWindow==GUI_WINDOW_SETTINGS) {
     settingsOpen=true;