Welcome to Chorister
Chorister is a free and open source (FOSS) web app to help you organize a choir, orchestra, band, or even solo musical performances. To simply things, this documentation will assume a choir, with a choir master and members.
Log learning progress
The key concept of Chorister is that every member has an account, and regularly (at least after every rehearsal) uses a simple feedback form to log their progress on the parts assigned to them:

Track performance readiness
This continued logging of members' learning progress allows to see the readiness of individual members, parts, and the entire group with regard to upcoming concert performances.

In addition to the overall confidence, a trend is calculated from the week-over-week changes, as well as an estimated performance readiness date, from extrapolating the learning velocity.

Plan rehearsals
The auto-curriculum feature suggests what to focus on in the next rehearsal, based on progress, learning velocity, and approaching deadlines. Just confirm with a few clicks!

Rehearsal recap
Attach comments and audio recordings to past rehearsals to keep track of your progress.
Attendance tracking
When a rehearsal is on, a QR code is shown for group leaders that members can scan to "check in" to the rehearsal. If someone is absent, they can submit a reason like illness, vacation, travel, etc. A history of attendance is thus maintained for every member.