Hi Pas,
there is currently no free offering like the HCP trial. At the moment the only option you have is to use the Cloud Appliance Library and the SAP Netweaver 7.40 SP08 offered there (SAP Cloud Appliance Library). The Netweaver image itself is for free but you have to have an AWS or Azure account where computing costs will arise. There is also a Netweaver 7.50 image but this image is not for free.
There was also a local Netweaver 7.40 image, but the download expired. According to the page a Netweaver 7.50 image is under preparation, but there is no date announced when this will be available (SAP NetWeaver AS ABAP 7.40 SP8 - Developer Edition to Download).
BR
Christian