alternative to TotalTerminal that works with El Capitan
If you're willing to disable System Integrity Protection to continue using TotalTerminal, you can do that. If not, the developer of TotalTerminal says the reason he stopped working on it is that he switched to iTerm 2, which he says "offers similar functionality to Visor and comparable features to build-in [sic] Terminal.app." I've never used either, but another question on this site explains how to set up iTerm to work in a similar manner.