Software that achieves my goal in a focused manner is something i typically enjoy. I don't want it to do everything under the sun, i want it to do one or two things well.
These days, to me, a "lightweight" alternative to Dropbox would be one that focuses on filesharing with none of that other junk.
The other quality of flexible composable systems is that they can be extended with something akin to an AoP system. Non-essential qualities can be woven and applied during composition so that each component doesn't have to implement various features.
A counter example is the find command, it has to implement a predicate language into the tool itself. If it omitted typed objects, a filter engine could select the subset. If find implemented polymorphic values, the predicate would dictate what facets were populated in the structures themselves but our shells don't work that way. A metashell that could define its environment and the streams of structures flowing between components could get us closer to a pervasively composable mode of system construction.
Unix pipelines [2] are awesome, but they aren't the pinnacle. I feel like all of us fall short in creating systems that compose. Most (scalable) systems should be fractal, while most composition is limited to a narrow first-order mode of operation.