Yes there is. Just extract it on Windows and use under Linux. Or you can get the necessary files from here:

https://github.com/martinpaljak/oracle_javacard_sdks

Building applets on Linux is simple as well:

https://github.com/martinpaljak/ant-javacard

No, there aren't any official releases for Linux anymore to my knowledge. Neither are the Ant commands supported anymore. I wish there were, but they seem to have been sunk. You might want to nicely ask your vendor, as the manufacturers have direct influence in the Java Card Forum. In the end the Java Card SDK is an Oracle product though, so they have the final say.

Note that all functionality is contained as platform independent within JAR files, and that the Java Card API runtime itself doesn't depend on the host platform either. It is therefore perfectly possible to create ant files and / or shell scripts based on the batch files delivered by the Java Card SDK. Look for more info at the answer of Martin Paljak.

I can provide this simple wrapper script (add it to the bin directory of the Java Card SDK as _starter.sh and make it executable):

#!/bin/bash

export JC_CLASSIC_HOME="$(dirname "$0")/../"

for l in "$JC_CLASSIC_HOME/lib"/*.jar ; do
    JC_CLASSPATH="$l:$JC_CLASSPATH"
done

MAIN="$1"
shift 1
java "-Djc.home=$JC_CLASSIC_HOME" -classpath "$JC_CLASSPATH" "$MAIN" "$@"

Then you can create individual launcher scripts utilizing this wrapper in the same directory:

capdump.sh:

#!/bin/bash

"$(dirname "$0")/_starter.sh" com.sun.javacard.capdump.CapDump "$@" 

capgen.sh:

#!/bin/bash

"$(dirname "$0")/_starter.sh" com.sun.javacard.jcasm.cap.Main "$@" 

converter.sh:

#!/bin/bash

"$(dirname "$0")/_starter.sh" com.sun.javacard.converter.Main "$@" 

exp2text.sh:

#!/bin/bash

"$(dirname "$0")/_starter.sh" com.sun.javacard.converter.Exp2Text "$@" 

verifycap.sh:

#!/bin/bash

"$(dirname "$0")/_starter.sh" com.sun.javacard.offcardverifier.Verifier "$@" 

verifyexp.sh:

#!/bin/bash

"$(dirname "$0")/_starter.sh" com.sun.javacard.offcardverifier.VerifyExp "$@" 

verifyrev.sh:

#!/bin/bash

"$(dirname "$0")/_starter.sh" com.sun.javacard.offcardverifier.VerifyRev "$@"