The only thing I can find on their homepage are Humble widgets which could theorethically give you also DRM-free versions but they decided to use Steam keys only.
I made exceptions but generally I won’t support developers who are OK with using DRM.
There is at least hope since the deal with SEGA comes to an end:
Ron wasn’t so sure about if the extra work of making new up-to-date builds for different distribution platforms will be worth it but at least Double Fine is known for putting their self-published games on DRM-free platforms like GOG and recently itch.io.
There may have been a similar deal regarding Costume Quest 2.