MacSwear is a better native port of Swear for Mac OS X. It uses OpenGL and a Cocoa GUI. It runs much smoother than the Allegro-based version of Swear, and it has some small graphical improvements.
The source is provided, and while the GUI part of it is heavily OS X-centric, the game part is written in plain C++ and OpenGL, and should be quite portable. I would very much like to see the game ported to other platforms, so I would be very grateful if somebody did this for me!
MilkSnake is an updated version of this same basic game, but with much improved graphics, and with music and sounds!