SAI format is proprietary and featured exclusively in the Paint Tool SAI and it does not seem likely that it is supported in other graphics editor. The program itself allows export to standard bitmap pictures (.bmp) and also to few Photoshop formats, namely .psd and .psb graphics.
Convert Paint Tool SAI drawing to Standard Windows bitmap image.
We found one software available in the database for this conversion.
Microsoft Windows software - convert sai to bmp on Windows
A painting software
Convert from sai file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.