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The standard bitcoind/bitcoin-qt client lets you ask for the highest known block, via RPC, or get notifications when a new 'best block' is locally acknowledged (via the -blocknotify option).
But, is there any way to tell when more than one equally-high blocks are circulating, and thus it's not yet clear which will win? Or does the standard client remain locked onto only the first block it receives, until it receives a definitively-longer chain?
I don't think the block height on it's own is sufficient information. You would probably need to examine the hashes, nonces and merkle, from different peers. – T9b – 2014-02-17T18:58:25.450
Even if you write the code for that you will probably want at least two instances running in antipodal points so the information that is propagated to them will be slightly different at these times of competing best-blocks. – George Kimionis – 2014-03-22T19:56:45.807