I used to be in the top 3% of contributors of hours to computation for BOINC projects, but I haven't been able to run BOINC for years. It seems it's not compiled for more traditional POSIX-type operating systems anymore, there hasn't been an update in years, and the source's compilation instructions are incomplete. I'm disappointed, compared to the early years of BOINC. This is the error I get.

/usr/local/lib64/boinc/boinc: /lib64/libssl.so.1.0.0: no version information available (required by /usr/local/lib64/boinc/boinc)
/usr/local/lib64/boinc/boinc: /usr/lib64/libcurl.so.4: no version information available (required by /usr/local/lib64/boinc/boinc)
/usr/local/lib64/boinc/boinc: /lib64/libcrypto.so.1.0.0: no version information available (required by /usr/local/lib64/boinc/boinc)

I don't think it's standard to have a path starting from root ‘/lib64.’ I don't know what the problem is with the other, libcurl, but that file is there, and more likely was something done with the compilation of BOINC rather than Slackware, which is arguably the #1 computer programming/science development system.

Actually, as I suspected, a knowledgeable Slackware user/programmer said, also according to a LinuxQuestions.org Slackware forum thread, the above error isn't as it may seem, some sort of non-traditional directory structure, but is that the stable version of BOINC now uses an outdated C++ application programming interface (API.) When is the next version going to finally be out?

Despite the source's (7.6.32) incomplete instructions, I was able to compile the main program, after doing something the instructions didn't say, and later making sense of the two URLs it links to that have conflicting information. When following one of those that made more sense, I was able to compile more stuff... except the BOINC manager. It looks like the source tries to compile it but doesn't have its own files (I didn't use ‘--disable-manager,’ there is just some source and/or Makefile problem.)

I'd like to use 7.6.32 but am not going to run it without the manager on my PC... maybe if I had a server I'd want to use for BOINC.

Can you point me to the documentation that has conflicting information?

Also the compilation instructions didn't change for a long time.
Here is the list of libraries that you need in order to compile: http://boinc.berkeley.edu/trac/wiki/SoftwarePrereqsUnix
Here is the explanation of how to build: http://boinc.berkeley.edu/trac/wiki/BuildSystem which basically boils down to:

git clone https://github.com/BOINC/boinc boinc
cd boinc
git checkout client_release/7.6/7.6.32
./_autosetup
./configure --disable-server
make

Which version of Slackware did you try this on?

Slackware (64-bit) 14.2, which has all the libraries you need for this, or are available from a quasi-official source. Boinc source INSTALL (incomplete) http://boinc.berkeley.edu/trac/wiki/CompileClient , http://boinc.berkeley.edu/trac/wiki/BuildSystem (all three say quite different things.)

Wasn't it clear now all I have to build is the manager? When I follow instructions on one of the URLs in the INSTALL file, rather than that file (which conflicts with both in describing configure) except I also add ‘--enable-manager’ to configure, make just has the following error: ‘cp: cannot stat '../../../stage//usr/local/bin/boincmgr': No such file or directory.’ So, INSTALL is incomplete (doesn't say to make) and you have three conflicting sets of instructions that don't describe all situations well, and some sort of problem with the source that they won't do what seems right for some/all of those instructions.

Yes, the INSTALL file is outdated. You should ignore that. But I don't see a problem with CompileClient and BuildSystem. The first just gives more examples while the second explains all the available options. To see if it can be compiled it is sufficient to use the commands I posted.

You also need to build the Client and the Manager. The first does the computation the second is the GUI to control the first. It seems that the Manager can not be build in your case. There must be some other build error that prevents this. You could check the config.log for any error or warning messages. I found out that the wxWidgets library is mostly the problem when the Manager can not be built.

I tried to compile the Client and Manager on Slackware 14.2 myself. It is missing the wxWidgets library but ./configure doesn't complain loudly about that. I then installed wxGTK3 from SlackBuilds which started the Manager compile but failed because the webview component is not found. this is nowadays included in webkitgtk3 which requires libwebp. I could install the second but the webkitgtk3 is giving me problems. I'm trying webkitgtk next as it seems the wxGTK3 library is compiled using GTK+2.