[nx]

Would be really cool if one could define "new gates" in terms of gates, e.g. a half-adder, a full-adder.

[nazgulnarsil]

agreed. a couple slots for your own black boxing of a component would enable fairly complex ideas to be quickly demonstrated. Could be a great teaching tool.

[likpok]

Indeed. In the CS architecture class here they use Logic Works, which is only a little higher-level, but with a much worse interface.

It is no replacement for more powerful things (e.g. FPGAdvantage), but for didactic purposes, this is quite useful.