When a travelling companion of mine had their passport stolen in South Africa, the NZ High Commission issued a ETD (Emergency Travel Document). This was a substitute for a passport.
However, if the government has revoked a passport, they're unlikely to issue such a document.
So then you're left with a few other methods.
In some places, national ID cards are fine to travel internationally - including the Economic Community of West African States, most of the EU (and some nearby countries) with the Schengen Area, the Cooperation Council for the Arab States of the Gulf, and Mercosur (in South America).
US Citizens can travel to Puerto Rico with just a photo ID.
According to Wikileaks, Edward Snowden has been issued with a type of emergency refugee document by Ecuador. Several countries issue similar documents, including the UK and even the US, who has a document called an I-94, which many other countries will recognise as a valid form of ID for transiting to the US. Even the International Red Cross is capable of issuing similar documents, although it's up to each country to decide whether to accept these.
Finally, if you're the head of state, like Queen Elizabeth, you may not even need a passport.