Qstit is described as 'Free software to project and manipulate electronic subtitles live, on film projections, theatre and other events (also called surtitles, supertitles, or soft-titles)' and is an app in the Video & Movies category. There are three alternatives to Qstit for Mac, Online / Web-based, Vagrant, Windows and Linux. The best alternative is Amara, which is free. Other great apps like Qstit are Subtitles for theatre (Freemium) and Subtivals (Free, Open Source).
Spend your time focusing on quality of your play, not on tech problems. Adding and translating new surtitles is fast and allow collaboration of multiple people. Change font, its size, colors and position of text at screen at once.