Lots of them.

All research of Interlisp-D, Smalltalk and Mesa/Cedar at Xerox PARC:

https://archive.org/details/bitsavers_xerox

Stéphane Ducasse also maintains the original Smalltalk manuals on his legacy books:

http://stephane.ducasse.free.fr/FreeBooks.html

Oberon at ETHZ:

http://www.ethoberon.ethz.ch/books.html

If you want to see how the latest incarnation of Oberon used to look like:

http://www.progtools.org/article.php?name=oberon&section=com...

For Modula-3 it is a bit harder, because of DEC/Olivetti being acquired by Compaq, which was then acquired by HP. So lots of sites are full with broken links.

So the older books are a better source than the Internet.

But still you can get some info here:

http://www.modula3.org/

http://ftp.labs.hp.com/ftp/pub/dec/SRC/

http://www-spin.cs.washington.edu/

Burroughs overview:

http://www.smecc.org/The%20Architecture%20%20of%20the%20Burr...

It lives on as Unisys MCP mainframes. There are some more informations when searching for it.

Algol-68RS used at Royal Navy:

https://en.wikipedia.org/wiki/ALGOL_68RS

This is just a small taste. If one cares about history of computing there are lots of other resources scattered around the web and libraries.