Broadcast raw transaction without input validation
Turns out there are many ways to do this:


Node.js: Bitcore lets you broadcast a raw transaction to the network without any kind of validation, see the "broadcast a transaction through P2P" example.
Python: Protocoin is a library that can do that.
Java: BitcoinJ can do it.
C#: Bitcoincsharp, which is a port of BitcoinJ can also do it.