You have to assume that Dr. Blob is some kind of mad scientist experimenting on microbia that are so feisty and dangerous that he finds it necessary to mount high-powered weapons around the rim of his Petri dishes so that when they get out of control and threaten to escape, he can unleash awesome energy beams to prevent them entering our environment and destroying the entire human race by infecting us with anthrax leprosy pi or influenzAIDS or something.
Rich Carlson of Digital Eel maintains that it's "based on Conway's Game of Life", and maybe the organism in your Petri dish behaves as cellular automata, but it sure doesn't feel like playing around with Life (which despite the name is not a game at all, but a simple set of rules that produces emergent phenomena--no goals, which, as I've argued, is one of the defining characteristics of the game.)
Instead, well, it's a sort of shoot-em-up--perhaps feeling more like Tempest since you rotate your guns around the Petri dish blasting away. Powerups give you more powerful guns, but the organism evolves more threatening behaviors over time, too, for a pretty compelling, somewhat humorous, but pretty brainless level-based gameplay experience.
Anyway, Dr. Blob's was orginally a for-sale indie game, developed by Digital Eel and published through Cheapass Games, of all things, but in the Christmas spirit (or perhaps because sales have tapered off to the virtually nonexistent), Digital Eel has decided to releases it to the masses for free.
"Free" sounds pretty nice for a game that in 2004 won two IGF awards--for art and audio.
(Digital Eel also developed Plasmaworm and Strange Adventures in Infinite Space among others.)
On Life and Blobs
Correction: Guns are stationary. The petri dish and its contents are rotated.
- - - - - - - - - -
Blob co-designer, musician and sound person here. RC of Digital Eel.
I didn't program the game, so I only have a surface understanding of what is happening.
For those who are interested, blob generation and growth in the game is achieved using Conway's rules.
http://www.math.com/students/wonders/life/life.html
The petri dish is a 49x49 grid of cells (with the corners cut off --the dish is circular). When the dish is rotated obviously the grid and everything on it is rotated.
Small patterns, randomized, 4x4, 5x5, etc., are generated under a nucleus --note that nuclei move around the grid (except in level 1), and that nuclei may split (mitosis!), etc. Blobs don't peter out because these small patterns are constantly being generated from their "center" (nucleus).
The whole thing iterates at a rate of 1/10 - 1/50 of a second (depending on which level is being played and whether the "frenzy" blob ability is in effect). So blobs are constantly moving and growing.
Blob destruction occurs when the mass of growing Life is destroyed by gunfire enough to afford clear shots to hit the nucleus, which has hit points.
A "marching squares" algorithm draws a kind of rounding shell around the cells which gives the blob its smooth fluid look.
You can actually see various life patterns emerge, though usually only the basic ones can be seen (because the grid is small and fills easily); blocks, beehives, oscillators and gliders.
Gliders are the best. ; )