There used to be DMIDI (distributed MIDI), it's even an IEEE standard. There were free windows (I think receive-only, not quite finished) and mac binaries but the author seems to have discontinued the website and google cannot find the stuff anymore.
Anyway implementing MIDI over LAN is nothing magic. You read data from a local virtual MIDI port send it via network (TCP or UDP) to the destination which forwards it to a virtual MIDI port (like midiyoke etc) which can be connected to any application.
I estimate about 10 days max (with Windows and OS X GUI) of development for a such a midi over ethernet tool.
I wonder why there's not a free version around or someone selling it at a cheap price. Seems developers are either lazy or not skilled enough
BTW: Do you think cross platform support is often needed ?
Eg having a Mac sending midi over ethernet to a PC and viceversa, or are such tools mostly used between PC-PC or Mac-Mac ?
But you never know .... perhaps soon such a tool will be freely availabe ....
There must be some alternative... Are there any known to be in develeopment?
Perhaps you could convince Benno to develop one for you. It would only take about 10 days as per his estimate. You could be a beta tester (so you could possibly get it for free) and then he could sell it at a much reduced price from MOL to cover his 10 days of development.
Christian, I know that you have a higher cost on MOL because you're running 6 computers but I know of no other alternative. As Daryl said, it is much cheaper than having MIDI interfaces and cables for each of your PC's (which is what you would need otherwise) and it works well. I know you're trying to save money where you can (we all do that) but the "works well" is usually the most important part for me.
Since I like if I can help to ease people's frustration here's the deal:
Let me cook up something in the next days ....
I already put together a semifunctional GUI this afternoon.
I'm not going to sell those small tools because I believe they are first too trivial and second I don't think one can earn that much from them. Handing out small gifts is sometimes much more gratifiying than a bit of pocket money
Ok back to the technical stuff: I have to make some internal tests and benchmarks before releasing something about the MIDI timing stability of Windows but I think midi over ethernet is easily doable.
Since one of the LinuxSampler developers is an expert in OS X audio/midi I'll ask him to add Mac support too so that the tool becomes cross platform.