<s>
A2	B-Application
(	O
formerly	O
named	O
Active	O
Object	B-Language
System	I-Language
(	O
AOS	O
)	O
,	O
and	O
then	O
Bluebottle	O
)	O
is	O
a	O
modular	O
,	O
object-oriented	B-Application
operating	I-Application
system	I-Application
with	O
unconventional	O
features	O
including	O
automatic	O
garbage-collected	B-General_Concept
memory	O
management	O
,	O
and	O
a	O
zooming	B-Application
user	I-Application
interface	I-Application
.	O
</s>
<s>
It	O
is	O
free	B-License
and	I-License
open-source	I-License
software	I-License
under	O
a	O
BSD-like	B-Operating_System
license	O
.	O
</s>
<s>
A2	B-Application
is	O
the	O
next	O
generation	O
of	O
Native	O
Oberon	B-Language
,	O
the	O
x86	B-Operating_System
PC	O
version	O
of	O
Niklaus	O
Wirth	O
's	O
operating	B-General_Concept
system	I-General_Concept
Oberon	B-Language
.	O
</s>
<s>
It	O
is	O
small	O
,	O
fast	O
,	O
supports	O
multiprocessing	B-Operating_System
computers	O
,	O
and	O
provides	O
soft	O
real-time	B-General_Concept
computing	I-General_Concept
operation	O
.	O
</s>
<s>
It	O
is	O
entirely	O
written	O
in	O
an	O
upward-compatible	O
dialect	O
of	O
the	O
programming	O
language	O
Oberon	B-Language
named	O
Active	B-Language
Oberon	I-Language
.	O
</s>
<s>
Both	O
languages	O
are	O
members	O
of	O
the	O
Pascal	B-Application
family	O
,	O
along	O
with	O
Modula-2	B-Language
.	O
</s>
<s>
A2	B-Application
's	O
design	O
allows	O
developing	O
efficient	O
systems	O
based	O
on	O
active	O
objects	O
which	O
run	O
directly	O
on	O
hardware	O
,	O
with	O
no	O
mediating	O
interpreter	B-Application
or	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
Active	O
objects	O
represent	O
a	O
combination	O
of	O
the	O
traditional	O
object-oriented	B-Language
programming	I-Language
(	O
OOP	O
)	O
model	O
of	O
an	O
object	O
,	O
combined	O
with	O
a	O
thread	B-Operating_System
that	O
executes	O
in	O
the	O
context	O
of	O
that	O
object	O
.	O
</s>
<s>
In	O
the	O
Active	B-Language
Oberon	I-Language
implementation	O
,	O
an	O
active	O
object	O
may	O
include	O
activity	O
of	O
its	O
own	O
,	O
and	O
of	O
its	O
ancestor	O
objects	O
.	O
</s>
<s>
Other	O
differences	O
between	O
A2	B-Application
and	O
more	O
mainstream	O
operating	B-General_Concept
systems	I-General_Concept
is	O
a	O
very	O
minimalist	B-Device
design	O
,	O
completely	O
implemented	O
in	O
a	O
type-safe	B-Language
language	O
,	O
with	O
automatic	B-General_Concept
memory	I-General_Concept
management	I-General_Concept
,	O
combined	O
with	O
a	O
powerful	O
and	O
flexible	O
set	O
of	O
primitives	O
(	O
at	O
the	O
level	O
of	O
programming	O
language	O
and	O
runtime	B-Device
system	I-Device
)	O
for	O
synchronising	O
access	O
to	O
the	O
internal	O
properties	O
of	O
objects	O
in	O
competing	O
execution	B-General_Concept
contexts	O
.	O
</s>
<s>
Above	O
the	O
kernel	B-Operating_System
layer	O
,	O
A2	B-Application
provides	O
a	O
flexible	O
set	O
of	O
modules	O
providing	O
unified	O
abstractions	O
for	O
devices	O
and	O
services	O
,	O
such	O
as	O
file	B-Application
systems	I-Application
,	O
user	B-Application
interfaces	I-Application
,	O
computer	B-Architecture
network	I-Architecture
connections	O
,	O
media	B-General_Concept
codecs	I-General_Concept
,	O
etc	O
.	O
</s>
<s>
Bluebottle	O
replaced	O
the	O
older	O
Oberon	B-Application
OS	I-Application
's	O
unique	O
text-based	B-Application
user	I-Application
interface	I-Application
(	O
TUI	O
)	O
with	O
a	O
zooming	B-Application
user	I-Application
interface	I-Application
(	O
ZUI	B-Application
)	O
,	O
which	O
is	O
significantly	O
more	O
like	O
a	O
conventional	O
graphical	B-Application
user	I-Application
interface	I-Application
(	O
GUI	B-Application
)	O
.	O
</s>
<s>
Like	O
Oberon	B-Language
,	O
though	O
,	O
its	O
user	B-Application
interface	I-Application
supports	O
a	O
point	O
and	O
click	O
interface	B-Architecture
metaphor	I-Architecture
to	O
execute	O
commands	O
directly	O
from	O
text	O
,	O
similar	O
to	O
clicking	O
hyperlinks	O
in	O
a	O
web	B-Application
browser	I-Application
.	O
</s>
