In addition to reader conditionals (#?(:cljs "ClojureScript" :clj "Clojure")),
it looks like it has almost 150 new functions and macros available:
array-map
as->
assoc!
bit-count
bit-shift-right-zero-fill
booleans
byte
bytes
case
cat
char
chars
chunked-seq?
clj->js
clone
cloneable?
comparator
completing
cond->
cond->>
conj!
dedupe
default-dispatch-val
disj!
dispatch-fn
dissoc!
divide
double
double-array
doubles
eduction
ensure-reduced
ex-cause
ex-data
ex-info
ex-message
filterv
float
floats
hash-keyword
hash-set
if-some
ifn?
implements?
indexed?
int
int-array
into-array
ints
iterable?
js-invoke
js-mod
js-str
key
keyword-identical?
lazy-cat
list?
long
long-array
longs
macroexpand
macroexpand-1
make-array
mapv
memfn
nchecked-dec-int
nthrest
obj-map
object-array
object?
persistent!
pop!
print-str
println-str
prn-str
prn-str-with-opts
random-sample
reduce-kv
reduceable?
reduced
reduced?
regexp?
reversible?
rseq
rsubseq
seqable?
sequence
short
shorts
shuffle
simple-benchmark
some->
some->>
some?
sorted-map
sorted-map-by
sorted-set
sorted-set-by
sorted?
special-symbol?
specify
specify!
subseq
test
to-array-2d
transduce
transient
unchecked-add
unchecked-add-int
unchecked-byte
unchecked-char
unchecked-dec
unchecked-dec-int
unchecked-divide-int
unchecked-double
unchecked-float
unchecked-float
unchecked-inc
unchecked-inc-int
unchecked-int
unchecked-long
unchecked-multiply
unchecked-multiply-int
unchecked-negate
unchecked-negate-int
unchecked-remainder-int
unchecked-short
unchecked-subtract
unchecked-subtract-int
unreduced
unsafe-bit-and
unsigned-bit-shift-right
update
val
volatile!
volatile?
vreset!
vswap!
when-some
with-out-str
with-redefs