[mtford]

I know a few of the investment banks have this kind of thing internally, implemented as a DAG: http://en.wikipedia.org/wiki/Directed_acyclic_graph. Cool stuff.

[agumonkey]

Many reactive dataflow programs are DAG based (at least most major 3D/CGI packages are). Simple and powerful.

[seanmcdirmid]

My reactive programming language can handle cyclic dependencies; DAGs are too inexpressive for general use (e.g. iterative computations). Getting that to work correctly is kind of scary though (especially when non-monotonic change is also supported).