Done:

  arena scrolling
  automake
  transparency
  pngs
  collisions
  ball source/target
  bitmap pool
  enemies (partial)
  weapons (partial)
  explosions
  air resistance
  tractor graphic (partial)
  tractor improvements (mass)
  exhaust graphic
  font
  screen window
  player status, player damage
  money
  shop/more weapons (partial)
  better collisions (player ship bounces wierdly)
  levels
  level descriptions
  player rescue collisions
  collision avoidance
  Title screen/game restart
  score
  switches+gates
  Make extra engines available in shop.
  Make bought equipment increase mass of ship 
  weapon graphics in shop
  Player energy/generators - make it so weapons/engines use energy when fired, make extra generators available in shop.
  invulnerability grace period
  
  (0.1 released)
  
  Sound: we can play sound now, but many events don't have suitable effects
  Hi scores
  Removed framerate-dependency
  Better (expensive) generators
  Windows version: it can build in mingw now!
  Better collisions (rockets won't pass through walls any more.)
  Hac^H^H^HFixed problems with collisions involving blocks under the shop
  Even more awesome weapons! (scatter shot)
  More levels

  (0.2 released)

  Fixed the Stupid AOE Bug: damage from area effects was based on the centre of
    the enemy - but some enemies, like the level 10 UFO, are so large that they
    can be *hit* by a rocket and yet not have their centre inside the blast
    radius, so they counted as outside its area of effect and took no damage.
    Doh!  Increased miner hitpoints so they won't chain-react under the new system.
  Improved framerate.  Mover-scenery collision detection was unbelievably slow,
    because it was unbelievably stupid.  Fixed this by doing a quick test first.
    Slowness and stupidity are now back at believable levels.
  Made it possible to load levels from text files
  Made collision direction work better (hitting the diagonal tiles was particuarly bad)
    All collisions seem reasonable now except for jamming the ship into a corner, which 
    behaves rather strangely
  Added some command line options (help, fullscreen, window, list directories)
  Proper installation (make install now works)
  Even more even more awesome weapons! (r.b.g, sniper)
  Added fireworks to hi score table.  Apart from looking nice, this helps indicate change in 
    state (input->display)

Not done yet:

Needed for version 4

  make shop more usable
  background
  Avoid ridiculously large bitmaps in the arena
  Even more even more awesome weapons! (scoop) 
  Save/load hi scores
  Level-dependent physics
  better error reporting when loading levels
  weapon configurations
  Clean up code



Do later:
  
  More levels
  More enemies

  Less hideous graphics (block.png and sink.png are particularly bad)
  more sound effects? (engine noise, level exit)
  Music ?

  Some sort of reward for finishing the game would be nice