The best open source alternative to VisualCron is AutoHotkey, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 10 alternatives to VisualCron and four of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to VisualCron are Sikuli (Free, Open Source), Cronicle (Free, Open Source) and PyGUIBot (Free, Open Source).
Cronicle is a multi-server task scheduler and runner, with a web based front-end UI. It handles both scheduled, repeating and on-demand jobs, targeting any number of slave servers, with real-time stats and live log viewer.