Any chance of porting this to Javascript?
Not really, no. The whole thing was designed with Python in mind.
Anyway, there are now some basic usage docs
here. I've also put in a basic Transaction Deserializer tool which can be upgraded with the functionality talked about earlier in the thread at a later time.
The most significant update is that you can now specify a "spending transaction" in the Stack Evaluator, and select one of its inputs. That input's scriptSig will be pushed to the stack before your script starts. "OP_CHECKSIG" and "OP_CHECKSIGVERIFY"
should work now.
Pretty soon I'll have to start incrementing the version number and providing changelogs.