The Egghe number is considered to be an improved alternative to the Hirsch number, at least to solve some problems the later has. The hindex ignores the number of citations to each individual article beyond what is needed to achieve a certain hindex. Hence an academic with an hindex of 5 could theoretically have a total of 25 citations (5 for each paper), but could also have more than a 1000 citations (4 papers with 250 citations each and one paper with 5 citations). In reality these extremes will be unlikely. However, once a paper belongs to the top h papers, its subsequent citations no longer "count". Such a paper can double or triple its citations without influencing the hindex (Egghe, 2006). Hence, in order to give more weight to highlycited articles Leo Egghe (2006) proposed the gindex. The gindex is defined as follows:
Given a set of articles ranked in decreasing order of the number of citations that they received, the gindex is the (unique) largest number such that the top g articles received (together) at least g2 citations.
Although the gindex has not yet attracted much attention or empirical verification, it would seem to be a very useful complement to the hindex. Here are the references (h* was proposed in 2005 and g** in 2006)  both are online:
* J. E. Hirsch, PNAS, Vol. 102, no. 46, 2005.
** L. Egghe, Scientometrics, Vol. 69, no. 1, 2006.
Finally this free software automatically computes both indexes: http://www.harzing.com/resources.htm#/pop.htm
