I want to learn forth now.
Where can I find a modern usable forth that works well on windows to make real programs?
Does such a thing even exist?
If you end up liking it and want 64bit, you can buy iForth for 100 EUR. It's what I use.
These are all amazing optimizing compilers.
If you care about OSS: Don't waste your time with GForth. If you want something simple that you can hack yourself, take a look at pforth.