ALPS is a per-application user-level proportional-share scheduler that operates with tow overhead and without any special kernel support. ALPS is useful to a range of applications, including scientific applications that need to control the CPU apportionment to the processes they create, to Web servers that need to limit the proportion of available CPU time given to spawned processes that service Web requests, and to middleware that supports multiple execution environments that are to run at different rates. ALPS works by minimally sampling the progress of processes under its control, and making simple predictions for when it should selectively pause and resume the processes. We present the algorithm, a UNIX-based implementation, and a performance evaluation. Our results show that the ALPS approach is practical; we can achieve good accuracy (under 5% error), and low overhead (under 1% of CPU), despite user-level operation