We present the Choir Singers Pilot, a web-based system that assists choir singers in their individual learning and practice. Our system is built using modern web technologies and provides singers with an interactive view of the musical score along with an aligned audio performance created using state-of-the-art singing synthesis technology. The Web Audio API is used to dynamically mix the choir voices and give users control over sound parameters. In-browser audio latency compensation is used to keep user recordings aligned to the reference music tracks. The pitch is automatically extracted from user recordings and can then be analyzed using an assessment algorithm to provide intonation ratings to the user. The system also facilitates communication and collaboration in choirs by enabling singers to share their recordings with conductors and receive feedback. Our work, in the larger scope of the TROMPA project, aims to enrich musical activities and promote use of digital music resources. To that end, we also synthesize thousands of public-domain choir scores and make them available in a searchable repository alongside relevant metadata for public consumption.