To digress a bit, Snood predates the whole casual game explosion, but in many ways presages it. As I wrote in 2003, Snood was, according to a Jupiter survey, the eighth most-played computer game in America--not the eighth best-selling, but number eight in terms of games people actually played on their computers, with Solitaire (aka Klondike) and Minesweeper occupying the top two slots, and conventional commercial games only showing up well down the list. Snood is still a game that goes under the casual game radar, because Dave Dobson, the creator, has never distributed it via the casual game portals--it's still pure shareware, but as such, has sold in the millions.
In all three games, you use the mouse to point a cannon, clicking it to release a round thingie of a particular color. They are essentially pick-3 games; if your thingie winds up connected to two or more thingies of the same color, they disappear, and other thingies hanging from them fall away, both the disappearing and falling thingies scoring you points. It's a surprisingly fun dynamic, and more challenging than most pick-3 games, as there's a billiards-like aspect to aiming your thingies, bouncing them off board edges, and landing them in precisely the right place. Not just scanning the board, ala Bejeweled, in other words, but with an element of player skill as well.
Where Splume differs from the earlier games is in its level design; in different levels, your shooter is at different sides of the screen, and sometimes you have two, shooting two thingies simultaneously. Sometimes there are objects in the middle of the screen you can't shoot through, and sometimes there are moving gizmos to which colored thingies are already attached. Swink and Wegner have obviously studied the earlier games, and looked for changes they can ring on the already established gameplay dynamic, which is one intelligent route to incremental innovation.
One other point worthy of note: Splume is built using the Unity 3D engine (and if you do not already have it installed, which you probably don't, you'll be asked to install the plug-in when you play--which you should do). Unity 3D is looking increasingly attractive as a development environment for indie developers of all sorts; not only is it capable of producing stand-alone 3D games of considerable complexity and merit (such as Global Conflicts: Palestine), and not only is it cross-platform (well, Mac and PC, no Linux support as yet), it can also be used to create web-playable versions like Splume. If I were developing something at present, I'd consider it a clearly better environment for web games than Flash, and competitive with things like Torque as a low-cost 3D engine. I suspect we're going to see a lot more games using Unity in future.