blobwars Metal Blob Solid episode 1 is a platform game in which you
have to collect MIA (missing in action) blobs scattered around many
areas.  There are other things to collect, keys to open doors, bosses
at the end of different levels, etcetera.  You can also re-visit levels
to collect things you missed earlier.

The program is GPL and the data (graphics etc) are free for use with 
this program, but not free for any other use.