Golly

For exploring cellular automata like the Game of Life.

Golly's key features:

Supports bounded and unbounded universes, with cells of up to 256 states. Supports multiple algorithms, including Bill Gosper's super fast hashlife algorithm. Many different types of CA are included: John von Neumann's 29-state CA, Wolfram's 1D rules, WireWorld, Generations, Langton's Loops, Paterson's Worms, etc. The RuleLoader algorithm lets you plug in new rules. Responsive even while generating or garbage collecting. Reads RLE, macrocell, Life 1.05/1.06, dblife, and MCell files. Can also read common graphic formats: BMP, PNG, GIF, TIFF. Can extract patterns, rules and scripts from zip files. Can download patterns, rules and scripts from online archives. Includes a state-of-the-art pattern collection. Can paste in patterns from the clipboard. Unlimited undo/redo. Configurable keyboard shortcuts. Auto fit option keeps patterns sized to the window. Full screen option (no menu/status/tool/scroll bars). Supports multiple layers, including cloned layers. HTML-based help with an integrated Life Lexicon. Scriptable via Lua or Python. Runs on Windows (XP+), Mac OS X (10.6+) and Linux (with GTK+ 2.x).