As for sites that have NeXT software...there are a number of them out there. Some with demo-only software, others with full-on versions with license details. Be aware that some of these may or may not be available any more.
fsck.technology --
https://fsck.technology/software/NeXT/
on nextcomputers.org, NeXT Files --
https://www.nextcomputers.org/NeXTfiles/
http://ftp.funet.fi/pub/NeXT
- the oldest archive still online from its original URL, the progenitor of the
nextcomputers.org excellent NeXTfiles archive. This was, I believe, put together by Joacim Mellin for the earlier NeXT hobbyist site
http://next.z80.org (how many folks here were on that?) and passed along to the founders of
nextcomputers.org...
http://nextcomputers.org/NeXTfiles
- our own excellent archive, with many more bytes of information added over the past decade+
http://nextcube.org - click download, then use 'me' and 'next' in the authentication window
- the OnionMixer archive
https://ftp.nice.ch
- the very nice archive of the former NeXT User Group in Zurich, Switzerland, I recommend it highly
http://next.haleblian.com
- Ray Haleblian's new archive, including KB7SQI's software split out as separate pkg or tgz files
http://www.nleymann.de/Nextstep/index.htm
- Nicolas Leymann's "Mini Archiv', incl. Amaya, the X11 html editor/web browser from the W3C (run it under CubX-Window or other NS X11 server)
http://www.wizards.de/~frank/franksprojects.html
- Frank Siegert's interesting collection of NS software, incl. a Columbia Appletalk Protocol pkg with a nice NextStep frontend
The
archive.org ftp archives contains an upload of Timothy Luomat's Peak Archive, formerly at
ftp://next.peak.org (this is where much of my NS software came from, many many moons ago)
https://fsck.technology/software/NeXT/NeXTSTEP Applications/
- Large collection of commercial NextStep software
Bonus: Documentation
NextStep User's Guide is available :
https://archive.org/download/ne-xtstep-user-guide-1994
https://www.scribd.com/document/372057826/Nextstep-User-Guide-1994
Network and System Administration Manual
http://www.cilinder.be/docs/next/NeXTStep/3.3/nsa/
http://www.nextcomputers.org/files/manuals/nsa
NextStep 3.3 Developer Documentation Manuals
http://www.cilinder.be/docs/next/NeXTStep/3.3/nd/
http://www.nextcomputers.org/files/manuals/nd/
Also avail. at
https://www.nextop.de
The latter two were produced by Randy Rencsok (look at
www.channelu.com in
archive.org ~2010). He also bought/sold NeXT hardware - I think I may remember he bought the CIA or NSA's supply when they stopped using NeXTs...
https://cdn.preterhuman.net/texts/computing/nextstep-openstep
- a fantastic archive of NeXT documents, incl NeXTAnswers
http://retro.haleblian.com/next/
http://www.bitsavers.org/pdf/next/