CasualConc has a very simple lemma handling feature.  All it does is simply reads a lemma file, such as Someya's e-lemma file, and use the information.

First, you need to prepare a lemma file in a UTF-8 plain text format. CasualConc accepts e-lemma format (lemma -> word,word,...) or list format (lemma word word word ... [simply separated by a single space]).  You can also specify a format of your own.  For more information, see Lemma in Preferences.  You don't need to include a form of word that is the same as lemma in the list.  For example, if you want to create a lemma for SEE, you will add a line:

see -> sees,seeing,saw,seen

Once you prepare a lemma file, go to Preferences -> Lemma and check Lemmatize under Lemma Handling. 

Now you can select the file you prepared.  Click Select Lemma File button to select the file.  You are ready to use the lemma file.

Lemma functions work differently in different tools.

Concord

In Concord, lemmatization is applied to a search word(s) and context word(s).  This is only applied if you turn on Apply Lemmatization to Search Word in Preferences.  If you enter a word or phrase, all the word forms of the words in the search word(s)/phrase(s) that are included in the lemma file will be searched.  For example, if you search context, CasualConc returns the concordance lines with  words in lemma context (context, contexts, etc.) as a keyword.

Cluster

In Cluster, if you turn on Lemmatization, the clusters on the list will be clusters of lemmas (not the actual words).  The actual word clusters included in the lemma clusters will be displayed along with frequencies in the column next to the frequency column.  If you turn on Apply Lemmatization to Search Word in Preferences, all the words in the same lemma will be searched just as Concord.  So if you search context, all the clusters that include the words in lemma context (context, contexts, etc.) will be searched.

Collocation

In Collocation, lemma handling is just like in Cluster.  The context words on the list will be lemmas and actual words will be displayed along with frequencies in the Lemmas column (scroll to the right).  If you turn on Apply Lemmatization to Search Word in Preferences, all the words in the same lemma will be searched just as Concord. 

Word Count

The word/n-gram list will be lemma/lemma-n-gram(?) list.  The words included in lemmas will be displayed in the column labeled Lemmaed Words.

 

These functions may or may not work as intended.  And the inconsistency of labeling is simply because I don't know how to label them.  If you have suggestions, please send them to me.