There's Capsicum for Linux[1]. Its a port of Capsicum[2] from FreeBSD to Linux. Capsicum was a joint project between the FreeBSD foundation, Cambridge and Google to create a hybrid capabilities framework. But Capsicum allows developers to do the same privilege dropping that pledge does. However Capsicum is more fine grained then pledge so its less easy to use. Also Capsicum for Linux is also out of tree currently.
[1]: http://www.capsicum-linux.org/ [2]: https://www.freebsd.org/cgi/man.cgi?capsicum(4)