The first suggested Java link on https://www.b4x.com/b4j.html fails when the download reaches about 39MB out of the 200+ supposedly in the zip file.
Repeatedly tried yesterday and today with same result.
Absolutely will not download in latest Firefox.
I finally got it on 3rd try in Edge.
Earlier Edge tries produced an odd small file in the form "Unconfirmed xxxx.crdownload," where xxxx is some number (error number?)
I am running completely up-to-date Win 10 64-bit and have not seen such download issues elsewhere.
Have you tried to click on "retry" after it fails? It will resume the download (it hasn't failed for me now but it can fail if there are network problems).