Donating to KiCad via The Linux Foundation is the preferred method of supporting KiCad development.
This support provides funds for project development and the developers behind it.
The Linux Foundation is a 501(c)(6) non-profit organization in the US.
Altium2kicad can help you migrate an Altium project to KiCad, it
supports most features of .PcbDoc and .SchDoc, so it can convert both
the PCB and schematic. It consists of a few perl scripts that are
executed on the altium design files.