Using a Raspberry Pi and either a 2-channel or a 6-channel Audioinjector board, combined with a low-cost GPS module to provide the timing, you can build yourself a multi-channel VLF SDR for timestamped signal capture. This is a headless device which you connect to via ethernet from Spectrum Lab (from Windows) or vlfrx-tools (from Linux), to receive multi-channel signals timestamped to an accuracy of better than 50 nanoseconds. The device also functions as a streaming audio server and NTP time server for your LAN, and runs an automatic whistler/aurora detector, a SID monitor, continuous signal recording, and retrieval of historic signal.
GPS timing of signals to accuracy better than a microsecond is essential if you're doing amateur radio work at VLF, for serious SID monitoring, for combining signals from multiple receivers, or for any kind of professional work at VLF.
These notes describe the hardware and software setup.