signal-desktop (Signal for Desktop)

Signal is an encrypted instant messaging and voice calling application
for Android, iOS, and the desktop. It uses the Internet to send
one-to-one and group messages, which can include images and video
messages, and make one-to-one voice/video calls.

This is a repackaging of the official binary .deb file distributed by
Open Whipser Systems.

WARNING:
Version 8.1.0 is the latest version able to be run natively on
slackware-15.0.  In order to run newer version, you need to upgrade
glibc packages from testing/packages/binutils-gcc-glibc on slackware
15.0.

If the version of glibc is too old (if you are running Slackware 15.0
without the testing glibc, it will be added to the /opt/Signal folder
and the binary will be patched to use it.

If you are running the testing glibc or slackware-current, the package
will be unmodified.

Thanks to Lumin and Yiannis for the slackware-stable workaround.