SIDPlayer is a replayer program for C64 music (SID tunes), running under BeOS and Unix. You can think of it as being a stripped-down C64 emulator that only emulates the CPU and the sound chip of the C64. SIDPlayer can be used as a stand-alone player or, under BeOS, as a plug-in for CL-Amp and SoundPlay.
TinySID is a very small SID player. Current features include 99% 6510 CPU emulation and fat 6581 SID emulation including filters (which sound different to other players). It has nothing to do with other projects such as SIDPlay, and the 6510/6581 emulation is based on routines by Tammo Hinrichs that have been further developed.