Over on YouTube Mike from the SDRplay team has created a tutorial video that shows how to use the SDRuno EXTIO edition. SDRuno is the official software of the SDRplay line of products and can be freely downloaded from the SDRplay website. The EXTIO edition allows other non-SDRplay SDR units to freely be used with SDRuno. The only restrictions are that the maximum bandwidth is artificially restricted to 2.5 MHz and some DSP filters are missing.
In the video Mike shows how to set up the SDRuno workspace to work with an RTL-SDR dongle and demos reception of some signals. Note that the EXTIO dll file for the RTL-SDR mentioned in the video is the same one required for HDSDR, and can be downloaded from the dll table on the HDSDR website.
If you’re interested in more, Mike has a full SDRuno tutorial series available on the SDRplay YouTube channel which mostly focuses on usage with the SDRplay units, but could be applicable to the EXTIO version as well.