Paul Chapman's Glue project is producing some interesting results these days. Glue (or rather Glue 2) is a search program that finds "natural" constructions of singlets (indivisible p1 and p2 patterns) by starting with a target object -- usually a block -- and bombarding it with a p2 slow salvo of gliders.
'salvo' means that all the gliders come from the same direction; 'slow' means that glider #n+1 must not arrive until the reaction from glider #n's collision has settled down into stability or a p2 oscillation, and 'p2' means that the only timing constraint on the gliders is that an even or odd phase may be specified. (Many intermediate collision results contain blinkers, beacons, toads, or other p2 patterns, and a glider on a given input lane can interact with a p2 target in two possible ways.)
This is an example of a clever new MCell rule by Brice Due -- it shows not only the Smear but also the starting locations of the gliders and block, without changing anything about how Life actually evolves. Potentially a fairly useful trick for displaying this stuff. His notes also taught me a new way to do cell-state substitutions, with an MCell command I hadn't noticed (or at least realized the potential of). I had been doing the same task much more painfully by setting up whole new rules to do state conversions.
Here's another take on the same display problem: Koenig's annotation format allows for multiple layers in different colors, in a format that's backwards compatible with standard RLE (at least for most Life editors.) Click on the image to see the RLE: