For being a first alpha release... Well, second now, there are really a few bugs, and the game looks amazing and well polished. However, it looks like we can't delete machines from the ingame folder browser. Clicking on the bin will only delete the thumbnail, resulting in a "Thumbnail not found" file shown in the in-game save/load screen, and the machine will still be there, fully functional and loadable. 
The workaround is fairly simple: just delete the file from the game folder itself (Besiege_Data/SavedMachines/*.bsg)
Just thought I'd point this little bug out, thanks for taking your time to read.