<s>
Skim	B-Language
is	O
an	O
open-source	O
PDF	B-Language
reader	I-Language
.	O
</s>
<s>
It	O
is	O
notably	O
the	O
first	O
free	B-Application
software	I-Application
PDF	B-Language
reader	I-Language
for	O
macOS	B-Application
.	O
</s>
<s>
It	O
is	O
written	O
in	O
Objective-C	B-Language
,	O
and	O
uses	O
Cocoa	B-Operating_System
APIs	I-Operating_System
.	O
</s>
<s>
It	O
is	O
released	O
under	O
a	O
BSD	B-Operating_System
license	I-Operating_System
.	O
</s>
<s>
Within	O
its	O
first	O
year	O
it	O
managed	O
to	O
gain	O
a	O
small	O
fan	O
base	O
of	O
users	O
due	O
to	O
its	O
ease	O
of	O
use	O
and	O
features	O
which	O
allowed	O
some	O
flexibility	O
over	O
other	O
PDF	O
browsers	O
for	O
Mac	B-Application
OS	I-Application
X	O
.	O
</s>
<s>
Its	O
main	O
developers	O
were	O
also	O
responsible	O
for	O
another	O
popular	O
open-source	O
program	O
,	O
BibDesk	B-Language
.	O
</s>
