<s>
Echo	B-Language
is	O
a	O
web	B-Application
application	I-Application
framework	I-Application
created	O
by	O
the	O
company	O
NextApp	O
.	O
</s>
<s>
The	O
latest	O
iteration	O
,	O
Echo3	O
,	O
allows	O
writing	O
applications	O
in	O
either	O
server-side	O
Java	B-Device
or	O
client-side	O
JavaScript	B-Language
.	O
</s>
<s>
Server-side	O
applications	O
do	O
not	O
require	O
developer	O
knowledge	O
of	O
HTML	O
,	O
HTTP	O
,	O
or	O
JavaScript	B-Language
.	O
</s>
<s>
Client-side	O
JavaScript-based	O
applications	O
do	O
not	O
require	O
a	O
server	O
,	O
but	O
can	O
communicate	O
with	O
one	O
via	O
AJAX	B-General_Concept
.	O
</s>
<s>
It	O
is	O
free	B-Application
software	I-Application
licensed	O
under	O
the	O
terms	O
of	O
the	O
Mozilla	B-License
Public	I-License
License	I-License
(	O
MPL	O
)	O
.	O
</s>
<s>
Echo	B-Language
originally	O
started	O
as	O
a	O
request-response	B-Protocol
web	B-Application
application	I-Application
framework	I-Application
that	O
leveraged	O
the	O
Swing	B-Language
object	O
model	O
to	O
improve	O
the	O
speed	O
of	O
application	O
development	O
.	O
</s>
<s>
Through	O
the	O
use	O
of	O
the	O
Swing	B-Language
model	O
,	O
Echo	B-Language
was	O
able	O
to	O
employ	O
concepts	O
such	O
as	O
components	O
and	O
event-driven	B-Application
programming	I-Application
that	O
removed	O
much	O
of	O
the	O
pain	O
of	O
web	B-Application
application	I-Application
development	I-Application
.	O
</s>
<s>
In	O
late	O
2005	O
,	O
NextApp	O
formally	O
announced	O
the	O
release	O
of	O
their	O
new	O
Ajax	B-General_Concept
based	O
web	B-Application
application	I-Application
platform	O
,	O
"	O
Echo2	O
"	O
.	O
</s>
<s>
This	O
framework	O
built	O
on	O
the	O
concepts	O
of	O
Echo	B-Language
(	O
well	O
known	O
API	B-Application
,	O
total	O
web	O
abstraction	B-Application
)	O
but	O
delivered	O
the	O
additional	O
benefit	O
of	O
being	O
an	O
Ajax	B-General_Concept
environment	O
.	O
</s>
<s>
NextApp	O
believed	O
that	O
this	O
approach	O
brought	O
the	O
framework	O
extremely	O
close	O
to	O
the	O
capabilities	O
of	O
rich	B-Protocol
clients	I-Protocol
.	O
</s>
<s>
NextApp	O
also	O
claimed	O
that	O
this	O
reincarnation	O
of	O
the	O
Echo	B-Language
framework	I-Language
provided	O
dramatic	O
performance	O
,	O
capability	O
,	O
and	O
user-experience	B-Application
enhancements	O
made	O
possible	O
by	O
its	O
new	O
Ajax-based	O
rendering	B-Protocol
engine	I-Protocol
.	O
</s>
<s>
The	O
focus	O
of	O
this	O
evolution	O
was	O
to	O
move	O
away	O
from	O
generating	O
markup	O
on	O
the	O
server	O
side	O
,	O
and	O
instead	O
to	O
implement	O
rendering	O
peers	O
as	O
native	O
JavaScript	B-Language
objects	O
,	O
with	O
an	O
XML-based	O
state	O
synchronization	O
protocol	O
between	O
client	O
(	O
web	O
browser	O
)	O
and	O
server	O
.	O
</s>
<s>
This	O
was	O
developed	O
in	O
tandem	O
with	O
a	O
core	O
JavaScript	B-Application
framework	I-Application
,	O
providing	O
the	O
ability	O
to	O
define	O
inheritance	O
hierarchies	O
in	O
JavaScript	B-Language
in	O
a	O
way	O
familiar	O
to	O
developers	O
of	O
object-oriented	B-Language
languages	I-Language
.	O
</s>
<s>
Echo	B-Language
is	O
often	O
compared	O
to	O
frameworks	O
such	O
as	O
Google	B-Language
Web	I-Language
Toolkit	I-Language
(	O
GWT	O
)	O
as	O
both	O
Echo	B-Language
and	O
GWT	O
(	O
among	O
others	O
)	O
offer	O
a	O
programming	O
model	O
that	O
completely	O
abstracts	O
users	O
from	O
the	O
web	B-Operating_System
tier	I-Operating_System
.	O
</s>
<s>
However	O
Echo	B-Language
differs	O
substantially	O
from	O
GWT	O
in	O
the	O
way	O
it	O
interacts	O
with	O
JavaScript	B-Language
.	O
</s>
<s>
GWT	O
essentially	O
implements	O
a	O
subset	O
of	O
the	O
Java	B-Device
API	I-Device
in	O
JavaScript	B-Language
,	O
and	O
as	O
such	O
,	O
Java	B-Language
code	I-Language
is	O
compiled	O
to	O
JavaScript	B-Language
and	O
fully	O
executed	O
on	O
the	O
client	O
side	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
Echo	B-Language
has	O
offered	O
a	O
dual-stack	O
approach	O
since	O
version	O
3	O
.	O
</s>
<s>
Applications	O
can	O
be	O
written	O
in	O
JavaScript	B-Language
(	O
client-side	O
)	O
or	O
Java	B-Device
(	O
server-side	O
)	O
or	O
in	O
mixed	O
forms	O
.	O
</s>
<s>
Comparable	O
frameworks	O
include	O
Vaadin	B-Language
,	O
RAP	B-Language
,	O
ZK	B-Language
,	O
OpenLaszlo	B-Application
,	O
ICEfaces	B-Language
,	O
ThinWire	O
,	O
Apache	B-Language
Wicket	I-Language
,	O
and	O
jSeamless	O
.	O
</s>
<s>
jZeno	O
:	O
A	O
full-stack	O
application	O
framework	O
that	O
uses	O
a	O
highly	O
optimized	O
version	O
of	O
the	O
original	O
Echo	B-Language
framework	I-Language
as	O
rendering	B-Protocol
engine	I-Protocol
.	O
</s>
<s>
Aejaks	O
:	O
A	O
Jacl	O
layer	O
on	O
top	O
of	O
Echo2	O
to	O
easily	O
create	O
rich	O
web	B-Application
applications	I-Application
.	O
</s>
