Scheduling program or app for self-scheduling

[Leaderofthebanned]

I work in a critical access hospital where our nurses cross departments. Currently we use an Excel form to schedule so that we can make sure that each shift has xx amount of ER, OB and med/surg nurses. Is anyone using a program or app that works for them. Ideally I would like them to self schedule but I am unsure how that would work. Any advise is appreciated!