YAFU (Yet Another Factoring Utility) is a BOINC distribution wrapper around the YAFU command-line factoring suite — one of the most respected open-source integer factorization tools in number-theory community use. The CLI tool by Ben Buhrow is widely used for factoring numbers up to ~110 digits on a single machine; the BOINC project takes the harder cases (up to 149 digits) and farms them out across volunteer computers.
YAFU's specific mission is to keep pushing the Aliquot Sequence frontier. An aliquot sequence starts with a number, then repeatedly applies the proper-divisor-sum function: (n) → s(n) where s(n) is the sum of n's divisors excluding itself. Some sequences terminate at 1, some hit a perfect or amicable number and cycle, and others appear to grow unbounded — but the only way to know is to compute the next term, which requires fully factoring the current one. The Lehmer Five and other open sequences require factoring 130-150-digit numbers, far beyond what NFS@Home or independent factorers can handle alone.
YAFU complements NFS@Home: where NFS@Home runs the General Number Field Sieve on the very largest target numbers (180+ digits, often for the Cunningham Project), YAFU handles the steady stream of 100-149-digit candidates that emerge from aliquot-sequence work. Smaller individual numbers, but vast quantities.
YAFU runs without external funding — no university, no grant, no salaried administrator — and accepts donations via the project page. Its work units are CPU-only, run on Windows and Linux, and can be paused indefinitely. It's a pure example of mathematics-as-volunteer-computing: small infrastructure, deep specialization, indefinite open-ended progress.