You need AmigaMesaRTL v2.0 to use Mesa MUI class!
http://kcbbs.gen.nz/~jarno/

Mesa.mcc is created and maintained by 
Szymon Ulatowski <szulat@friko6.onet.pl>
support page: http://friko6.onet.pl/rz/szulat/mesamcc/

 PERMSSN    UID  GID    PACKED    SIZE  RATIO     CRC       STAMP          NAME
---------- ----------- ------- ------- ------ ---------- ------------ -------------
[generic]                  234     620  37.7% -lh5- c81a Sep 13  1998 demos.info
[generic]                 7016   11836  59.3% -lh5- fb94 Sep 13  1998 demos/AnimDemo
[generic]                  400     835  47.9% -lh5- 1846 Sep 13  1998 demos/AnimDemo.info
[generic]                 6146   11512  53.4% -lh5- 1aff Sep 13  1998 demos/LightDemo
[generic]                  401     835  48.0% -lh5- b55a Sep 13  1998 demos/LightDemo.info
[generic]                 7653   13080  58.5% -lh5- d999 Sep 13  1998 demos/TreeDemo
[generic]                  399     835  47.8% -lh5- 4122 Sep 13  1998 demos/TreeDemo.info
[generic]                  238     620  38.4% -lh5- e085 Sep 13  1998 libs.info
[generic]                 5450    8680  62.8% -lh5- 049e Sep 13  1998 libs/Mesa.mcc
[generic]                10038   19100  52.6% -lh5- df71 Sep 13  1998 libs/Mesa.mcp
[generic]                 5703    9364  60.9% -lh5- e455 Sep 13  1998 libs/Readargsgroup.mcc
[generic]                  395     599  65.9% -lh5- 127e Sep 16  1998 readme
[generic]                  307     831  36.9% -lh5- a2d3 Sep 13  1998 README.info
---------- ----------- ------- ------- ------ ---------- ------------ -------------
 Total        13 files   44380   78747  56.4%            Sep 22  1998